Hello,

If running as root, this will work. If not, add sudo before the commands.

apt-get remove --purge --auto-remove proftpd

Then you can search your droplet for the left over directories and files with these commands.

find -type d -name proftp
find -type f -name proftp

This will remove the directory and everything inside.

rm -rf /path/to/directory

Remove a single file.

rm /path/to/file

I hope this helps.

PS: Please take a snapshot first. Removing things from your droplet can be risky in some situations. If you delete the wrong directory or file, the world could come crashing down for you.