where do i set numbers of backup pr vm?

I don't know whats wrong with me, but all of a sudden i can't find where i set the number of backups to be made per vm.

I have a running backup where i want to ajust how many days back i want backup of my vms but i can't find it.

my proxmox version is 3.2-2

if i edit the job underdatacenter -> backup there is not entry for numbers of backup per vm