Gee - I wish I could, but the manual for this is... somewhere in a box after a move.

Refreshing myself with the review, it seems memory is dedicated per-device (and you can't delete individual hard buttons), so you'd only need to delete one entire device to deal with the "overload" error. This is done via the RESET button in the battery compartment.

Note that correct learning technique and not making any errors is about the only way to deal with the extremely limited memory on this 40-year-old remote.