Tenant change on existing lease

[Jeremy Jareckyj]

Hey Everyone! 

Had a quick question in regards to a tenant change. I have never come across this situation before so would love to get some feedback any who have!

I have two tenants on a lease right now for a single family home in Illinois. One tenant wants to leave mid-lease and replace himself on the lease with his cousin. 

Of course I plan to have the cousin apply just as any tenant would, but would you create an entirely new lease?