Does anyone know how difficult it is for an existing franchise to renew its contract with a franchisor? Does it happen automatically or is there some negotiation?

As long as your franchise has met the earnings expectations of the franchisor you should be fine

I agree if you are a good franchise for them it is to both of your advantage to keep going with the relationship.

The best place you can look is the ufoc - it will describe in detail what the renewal terms are.