This can be done by the proxy (you, I assume?) notifying the principal (who executed the POA) in writing that the proxy no longer wishes to serve. If the two aren't geographically close, the resignation can be mailed, by certified mail preferably.
It might be handled differently in NY. But this is how I've seen it handled in my state.
If you were appointed by a Judge in Surrogate's court, that court is where you send your resignation. If you were appointed by the individual, you resign in writing to them personally. ( I am a Guardian in NY)
It might be handled differently in NY. But this is how I've seen it handled in my state.