For ranks 1-20, you may
remove at any time, any piece of equipment (armor or weapon) that
would better your character. The only restriction is that you
must be able to use that equipment at the time you request it.
For all other ranks, to
remove an item from the bank, you must first donate an item of equal
or greater quality, ie: if you want a green item, you need to leave a
green item. If you want a blue item, leave a blue item.
The individual banks
may be a little more lax on the rules based on the amount of donations
taken in by an individual.
Guild banks have the
right to disenchant any items donated to the bank to help conserve
space and to help generate gold toward loans.
If the guild bank that
you want access to is not normally online when you are online, send an
in game letter telling them what you need and send the donation
requirement needed in that letter (when applicable).