What do I need to do if a donor changes the amount they give?
If a donor informs you of a change to their donation amount (or date they give / frequency they give), there is NOTHING that you need to do with this within ExpensePlus.
ExpensePlus remembers and quick-matches donations in an automated fashion, based on the bank description, not based on the date or amount. Therefore, there is no need to update anything if a donor changes either the frequency or the amount they give (which is why you won't find anything to update either within the memorized transactions screen or the manage donor screen).
If the donor gives an additional gift for a different purpose e.g. foodbank appeal, then again, this can simply be entered (and memorized) during bank matching. ExpensePlus remembers transactions per bank account and multiple donations can be remembered per donor (so ExpensePlus can remember 'Bob Jones Tithe' and 'Bob Jones Foodbank' and correctly allocate these donations to the corresponding funds/categories).
If the additional designated or restricted donation is made using an identical bank reference (and you've only been notified of the change externally outside the system), you will need to either exclude this donation prior to quick matching (from within the quick matching screen) or after quick-matching, manually edit and reallocate the donation.