Best Method to Raise Rents on Existing Tenants

[Demetrius Lindsey]

Hello BP, 

I am under contract on a 3 unit building. My wife and I are going to house hack. We are hoping to close on April 2nd and the current owner is going to do a rent back for two months. The dilemma is that the two other units are below market rents and we want to raise them. One tenant is brand new like a month the other has 6 months left on the lease. I am wondering how anyone goes about notifying and then implementing a rent increase after closing.