Raising rent on newly purchased property

[Andrew Headley]

I'm in the process of purchasing a multifamily unit. The one side is vacant and the other has a tenant. This tenant has lived there for 15 years and only pays $500 a month in rent. The rent in this area ranges from $700-900. I want to raise the rent to $700 but from what I'm reading I can't only increase the rent 10% a year. $550 then another year $605 and so on. Does anyone have any experience with this? Can I legally raise the rent to $700 when their current lease expires? This property is located in the state of PA. Any insight or other potential options would be greatly appreciated. Thank you for your time.