Full Hard disk, need delete something old backup files.

Dear all.

I'm implementation system with 10  VM window server2003/2008. I'm installing  BE 12.5 on 01 VM Window server  . set backup system state & C: Drive 

Backup from Mon-Sat is differentials , Full at Sunday . backup to D drive (D:\ drive 1TB mapping from storage) .

After over 01 week  the D:\Driver is full, I testing the backup file increate over 70GB for every 01 day . Now i need solution delete or setting to get space at D:\drive , i want backup file only 500 GB ?

Have you got any solution for this case ? pls advise

Thanks !

XuanP