It should not erase your existing presets. HOWEVER, you should always back up the unit before updating. Your worst case scenario right now would be that you would have to revert to the previous software and re-upload your presets from FactorLib.
I think this is a weird piece to leave out of such a big update that includes patch naming. Am I really going to spend hours naming and adjusting presets only to NOT be able to back them up before the next software release? No. Way.