Best way to increase rent

[Judy A.]

Looking for help. My husband and I are soon to be brand new landlords....My father in law recently passed away and we will be taking ownership of the home. It is a 2 family home in Boston(Dorchester), MA. His mother lives in one unit and rents out the extra bedrooms and the other unit is a 3br 1bath apt. The tenants pay 1200/month.  They also have a parking spot that is included with no extra charge. Rent in the area is well over 2k. How do we go about increasing the rent? Is it ok to increase the rent substantially to bring it to what the market is doing? If we do increase it do we just let them know 30 days before? They are long term tenants(been living there for years) and have a month to month lease. Thanks in advance!!!