Can son make different agreement if father (Owner) died

Dear Sir, I have a 1100 sq feet commercial room which was rented by my father to a businessman.The agreement papers were signed by my father only and the agreement is for 5 years that is till august 2020 . My father died last year due to heart attack.So My question is does the agreement holds any relevance now after my Father's death since I want to sell this property.And I am afraid that the tenant might not vacate the room even after my legal notice before 3 months.As they are financially very strong and can easily fight a case with me. Therefore I want to know that can the agreement done by my dad be considered null and void now and can I sign a separate agreement reducing the time period from 5 years to 2 years being the legal heir after my Father's death as I think this will ease me in selling the said property. Any guidelines sir. Thankx.