Changing electric plug fixtures outside plate that was painted over and pulled off - nothing fits
Removing cover plates that have been "stuck" to the drywall by being painted over can be fairly simple. I'd suggest purchasing a simple utility knife from your local hardware store and carefully running that around the edge of the plate where it meets the drywall. This will cut the paint membrane and prevent the painted drywall surface from peeling or tearing when you remove the plate. Once you've done that, just unscrew the plate and remove.

As for replacing the plate, there are oversized replacement wallplates available to conceal larger openings. Just search for "oversized outlet plate" online to see some examples.