When you downloaded the new firmware there were pdf files included to explain how to erase the loops.

FSW LOOP ERASE: Erase loops by first holding down the STOP/TAP FSW and then pressing the LOOP A FSW to erase Loop A or LOOP B FSW to erase Loop B. Once either loop footswitch is pressed the loop is erased, you do not have to hold the loop footswitches. The erase operation cannot be undone. If the 22500 Foot Controller is attached you could instead press the LOOP DOWN and LOOP UP FSWs—after pressing and holding the STOP/TAP FSW on the 22500 main unit—to erase Loop A and Loop B respectively.
Note 1: Pressing the STOP/TAP at the same time as a LOOP FSW will not erase the loop; STOP/TAP needs to be pressed before the LOOP FSW.
Note 2: A loop may be erased while idle, playing, recording or overdubbing.