Section 8 4 BR voucher for 5BR unit

I am in the process of buying a five-bedroom single family house and noted the tenants (who was placed by the old owner) has a 4 bedroom voucher but was placed in a 5 bedroom unit. I am wondering how difficult it is to get the current tenants out and replace with someone with a 5-bedroom voucher. Anyone insights you could offer would be greatly appreciated!