Cannot delete lifestream plugin via ftp

I’m trying to upgrade my wordpress, but have come upon an error similar to that of this forum:

https://www.ads-software.com/support/topic/upgraded-to-31-and-cant-access-anything

I’m trying to follow the suggestions there, but have hit another snag. Because I can’t access my admin, I’m disabling plugins via FTP. Lifestream is the only one left and it won’t be deleted, the following error pops up:

550 Can’t remove directory: Directory not empty.

I’ve deleted all visible contents of this file, but it still won’t delete and the error keeps coming up.

Help please!

Ps. New to wordpress, new to code, please use layman’s speak in yoru responses!

THANK YOU!