I have shadow protect on my computers at home. I have about 900GB as full images for my PC, and then incremental and I meant to set it up as a monthly job but set it up as a weekly. It won't allow me to change it, is there a way that I can change it or do I need to delete the old backups and recreate and re-backup the 900GB the first time again? 

I am running the latest version.