Hello Tafx,
I would advise to find out what is consuming the space first and then take steps to fix the cause. Automatic backups can be enabled only if you configured them via Plesk as they are disabled by default. To discover what can be eating up so many disk space you need to use SSH. The following page will help you to SSH into the server:
http://www.lunarforums.com/lunarpages_dedicated_web_hosting/how_to_login_to_your_dedicated_server_via_ssh-t26372.0.htmlThe root password for your VPS should be the same as you used on signing up for the plan.
Then, you need to switch to the root of the filesystem by inputing:
cd /
where "cd" is the command changing the working directory and / is where all Linux filesystems get mounted to. Then you can use the following command to ouput top 5 folders with with biggest disk usage and then cd to the largerst folder which will be listed on the first line and repeat this command to get more detailed path to the biggest folder:
du -s ./* | sort -rn | head -5
This command lists 5 largest folders at the current location.
Please advise, what folder you found to be consuming the space so the cause could be eliminated.