Help me figure out how to update to a newer iphone!

So I've been looking around here but couldn't find any situation similar to my own.

In July of 2012 I got my first iphone, a 4s that is still in good condition that I use today. However, in January of 2014 I got out of my contract for a good deal and updated to the iphone 5s. After only a little over a month of having that phone, I set it on top of my car and then proceeded to drive off into a busy street, never to find that phone again .

Well, after looking and looking for a few days I called up ATT and had my older 4s reactivated. Now, as I have had my 4s in my possession for nearly 2 years, I am interested in waiting a few months and then purchasing a 6 when it comes out.

My question is, will I be able to update my iphone because I purchased the 4s in July? Or, will I have to keep the 4s another full two years before having the chance to update, because I bought a new phone in January and had a contract for that.
Is there any way I will be able to buy a new contract for the iphone 6 without having to spend another 2 years on the soon to be outdated 4s?

Contact AT&T and ask them, otherwise buy an unlocked iPhone from Apple which you can then activate with a carrier of your choice. Nowadays most carriers are giving better deals on already purchased iPhones. You really do not save money by taking a 2 year subsidized contract with AT&T for a new iPhone 6. (whenever it comes out)