Raising rent on tenants after purchase of property -- good or bad idea?

[Chris Pasternak]

Title says it all. The additional details are that the top tenant has been there for 4 years and the bottom tenant has only lived there since August. I was wanting to raise the rent $50-$75 for the top unit (3 bed) and $25-$50 for the bottom unit (2 bed). The current rents are just too low.

Thanks all!