Rental property with tenants in place - how to go about adjusting the rents?

[Kay Nemen]

Hi all! I'm about to close on my first rental property (yay!) - a quadplex in the DFW area with all units rented below the market rent (about 20% below). How would you go about raising the rent - Would you wait for a few months or do it as soon as possible? All tenants are MTM with a good track history. The property should generate about $200/month in cash flow at the current rent. Obviously, it's going to put me in a safer spot if I raise the rent to market value, but this is also my first time dealing with a rental property out of state, so I don't want to come off too hard. There is a property manager in place, and I would like to keep using him. 

What do you guys think? 

Thanks in advance!!