FTP How to access

With both website and Word Press dashboard inaccessible because of fatal error caused by trying to auto update plug ins, the only help message I get is try to go through FTP and delete.
Can someone explain in words of one syllable what this is and how to access it? I’m reasonable computer savvy but only as a user, not a programmer. Help me please.

You can see the lock out white screen at
artinthepark.co.nz