Hi David Vieira,
There are many way to backup your site.
1. Use
http://www.akeebabackup.com/ for simple use
2. Manual download all files and export database to sql file and store them locally.
3. Copy and rename a folder (if you just need to backup the file of a folder)
After you backup your site. Just download the latest package on github and install via Extension Manager.
Then you can recompile CSS.
Regards