What version of Filemaker Server are you using?
In FMS 10, the number of retained copies is a setting in the back up schedule. Just use the admin console to bring up your schedules, double click the back up schedule to start the schedule assistant and click next to keep stepping through each part of the schedule set up. One field in the Schedule assistant is labeled Maximum Number of backups to keep. You can change this to control how many copies are retained before the oldest starts getting deleted with each new back up.
You can create a second back up schedule that runs "once every n days". If you specify once every 7 days, you'll get the weekly back up you've requested.
I use server 9 advanced, is this the same process?
As far as I know, it should be similar. I'd access the admin console on your server and take a look at its schedules to find out.
The FMS backup process has been changed drastically in 10. Prior to 10, you would have to set up multiple backup schedules.
You should create 7 seperate ( weekly schedule ) to backup into 7 different path locations.
IOW, create a seperate weekly schedule for each day to record into a different spot.