Buying a duplex am I obligated to keep current lease

[Lisa Lavine]

I would like to live in one unit but both are rented  one till next jan. and other till feb.2017
Do I have to abide by current lease 
And terms as they also allow pets.
I realize people are not going to keep lease I'd I  stop allowing pets 
But if I go in and see they are causing a mess . I am wondering, what are my 
Rights as owner/landlord
Looking to make offer today .
Any  response ASAP would be appreciated 
Thanks 
L&jr