buying a tenant occupied home

[Jared Pittman]

ok, so here i am analyzing some properties.  i want to buy a tenant occupied home and some of them are already in good cash flow shape, but for a couple others the rent needs to be raised, it seems low for the area as well as i need to raise it to account for a management fee, im not in this to be a landlord i have a job already.   

so my question is this, if i buy a property, is the lease null and void, are they protected from a raise in rent, if i raise the rent are they legally allowed to break the lease, if so that would defeat the whole purpose.  Any help on how to approach this would be great thanks.