BRRRR Help a new investor needing advice

[Alexandria Harden]

I am a fairly new investor looking to buy my first 8 unit apartment complex. I am buying locally from my real estate agent but the property is already fully rented out. How can I add value while they are in the units as well especially with the weather being as cold (Property is in Central Illinois). Also how do you go about redoing contracts with the ability to raise rents even though they have been in the property for awhile.