Q. 1. What does the Catholic Church teach about a person making a vow or promise to God?
A. 1. The Catholic Church covers the matters of vows and promises in # 2101 to 2103 of the Catechism.
# 2101 "In many circumstances, the Christian is called to make promises to God. Baptism and Confirmation, Matrimony and Holy Orders always entail promises. Out of personal devotion, the Christian may also promise to God this action, that prayer, this alms-giving, that pilgrimage, and so forth. Fidelity to promises made to God is a sign of the respect owed to the divine majesty and of love for a faithful God. [1237, 1064]"
# 2102 ""A vow is a deliberate and free promise made to God concerning a possible and better good which must be fulfilled by reason of the virtue of religion," [CIC, can. 1191 § 1] A vow is an act of devotion in which the Christian dedicates himself to God or promises him some good work. By fulfilling his vows he renders to God what has been promised and consecrated to Him. The Acts of the Apostles shows us St. Paul concerned to fulfill the vows he had made. [Cf. Acts 18:18; 21:23-24]"
# 2103 "The Church recognizes an exemplary value in the vows to practice the evangelical counsels: [Cf. CIC, can. 654] "
"Mother Church rejoices that she has within herself many men and women who pursue the Savior's self-emptying more closely and show it forth more clearly, by undertaking poverty with the freedom of the children of God, and renouncing their own will: they submit themselves to man for the sake of God, thus going beyond what is of precept in the matter of perfection, so as to conform themselves more fully to the obedient Christ. [LG 42 § 2] "
"The Church Canon Laws, in certain cases and for proportionate reasons, dispense from vows and promises [Cf. CIC, cann. 692; 1196-1197]"
Q. 2. The above references appears to refer to those who make religious vows. What about a lay person who made a private vow? What if I made a private vow and I no longer wish to uphold that vow? What do I do?
A. 2. Many, with all good intent, when they are young and zealous, they make a vow to God with the intention of keeping it for life. Not having consulted a spiritual director prior to making such a vow, they do not realize that a vow for life is a long time. Also, those who make private vows often walk a lonely spiritual life without the support that religious vocations find in Dioceses or religious Orders.
Such vows or promises may consist of a vow to remain celibate for life, a promise to be a missionary for life, a promise to pray the Rosary on a daily basis throughout one's life, a promise to never commit a certain sin, etc...
Knowing that many individual do make private vows and that some may want to be dispensed from such a vow during their lives, the Church covers this matter in the Canon Laws where it states:
Canon Law # 692 "An indult to leave the institute, which is lawfully granted and notified to the member, by virtue of the law itself carries with it, unless it has been rejected by the member in the act of notification, a dispensation from the vows and from all obligations arising from profession.""
Canon Law # 1196 "Besides the Roman Pontiff, the following can dispense from private vows, provided the dispensation does not injure the acquired rights of others;"
1° "the local Ordinary and the parish priest, in respect of all their own subjects and also of peregrini;"
(Note: "peregrini" means "travellers.)
2° "the Superior of a religious institute or of a society of apostolic life, if these are clerical and of pontifical right, in respect of members, novices and those who reside day and night in a house of the institute or society;
3° "those to whom the faculty of dispensing has been delegated by the Apostolic See or by the local Ordinary."
Canon Law # 1197 "What has been promised by private vow can be commuted into something better or equally good by the person who made the vow. It can be commuted into something less good by one who has authority to dispense in accordance with Canon Law # 1196."
(In simple English, # 1197 means "The person who makes a private vow can commute the work promised by the vow into a better or equal good; however, one who has the power of dispensing according to the norm of ? can. 1196 can commute it into a lesser good.)
To answer your question, private vows that are not associated with a Diocese or a religious Order, falls under the juridisction of the parish priest (see # 1196. 1° above). In order to have your private vow or promise replaced by something else of equal good or of a lesser good, please consult your local priest.