Asking Good Tenants To Leave?

[Shelby Pracht]

We have a duplex with solid, long term tenants in both units. However, we really want to move into one side ourselves! One tenant is paying significantly more than the other, but the one paying less has been there for 7 years already. How could we go about nicely asking one of them to leave, and which one should we ask!? Or is this just an awful idea and we should tough it out where we are?