Ubuntu won't let me edit or delete .vimrc file

User-specific changes like that should go in your personal .vimrc, which should be located in your home directory. If this file doesn’t exist yet you can simply create it. This will add your set line to ~/.vimrc creating this file if necessary:

echo 'set mouse=a' >>~/.vimrc

After that, either restart vim or source the file in a running instance with

:source ~/.vimrc

for the change to take effect.

When vim gives you this warning, it also should give you some options at the bottom:

[O]pen Read-Only, (E)dit anyway, (R)ecover, (Q)uit, (A)bort:

Chose "R" if you want to recover whatever changes and "E" if you don't.

If you persistently get this message, delete the swap file named.

More information is found in the error message normally.