if you don't want to scan the computer in weakly . you can scheduled the anti virus again as monthly .
but the monthly scanning is a long time , you will only know the status of the threats in the computer only once in the month. so to protect the computer from the threats . scanning should be scheduled in a weakly.
but you can scheduled according to you .
go to the programs >accessories>system tools> scheduled .
follow the intstruction and set the scheduled as you want.