2nd year for tenants what to do with deposit

Tenancy Types and Management

Apologies for what I expect is a really basic question.
I am about to offer a 2nd years AST to 5 students. I plan to re issue a new AST with a small rent increase but wondered what I should do with the deposit?
I took deposits from all of them last year, equivalent to 4 weeks rent and deposited it in the DPS. Do I have to give back the deposit for last year and then collect it again, re deposit it reflecting an increased amount or, alter my AST to state there is no deposit taken this time?
Thank you
Kate Ryan