Hi,
In reply to your questions:
1. where is the backup file located? i want to store it to some where else before i delete it in Plesk in order to make another newer backup.
The backup is made to the disk space of hardware node and you do not have access to it.
2. How can i make more than one backups?
Only one full backup is allowed on VPS plan. If you are going to perform major changes on the server, you can remove the current backup and create a new one so that you could get back if something goes wrong.
3. i could not find "pleskbackup" or "pleskresotre" utilites in my VPS.
You need to add Plesk backup component to get these features available. This can be performed under Server -> Updater. Select "Plesk Backup Manager" and click Install link.
I hope this helps.