Originally Posted by WineCountryUA

When you purchase a discount, non-refundable fare and then cancel, the monies remain with UA. There is no fee to cancel however to access the credit (base fare and fees and taxes) to purchase another ticket, there will be a fee (and this is new money - you can not deduct it from the credit) that varies based on the original ticket purchased. The new ticket must be purchased within a year of the purchase date of the original ticket and can only be for the same person.

If the new ticket does not use the entire credit, a credit voucher for remainder will be issued. You have one year from when it is issued to use and it can be used by anyone.

More details are in this thread's wiki.