Can I change my iphone 4 to iphone 5 without any contract violations?

If I were to switch my iPhone 4 to iPhone 5, would I be violating my contract since iPhone 5 is 4G LTE, but iPhone 4 only uses up to 3G.

Yes you can change phones no problem. There might be a small activation fee maybe but changing phones are perfectly fine. I've done it a dozen times

You can buy any phone that works on your carrier's network and activate it for your line. You just won't get it for new-contract pricing unless you're renewing you contract for another two years (which is usually only available about 3 or 4 months before your contract expires, or later).

No problem. You can use whatever phone you want as long as you continue paying for your present deal. But your iP5 only gets 4G where available and via the correct SIM. As your present deal is for a 3G contract, that's all your iP5 would be able to use.

To get 4G services you'd need to upgrade your contract. If you're supplying your own iP5 then it's highly likely that your contract provider would allow you to upgrade prematurely providing you pay the additional monthly fee for a 4G service. Note that unless you pay a lot extra that might mean you get fewer minutes, SMS, MMS and a smaller monthly data allowance than you've been used to, as 4G contracts usually squeeze those features in able to keep the pricing differential lower between 3G and 4G contracts; early adopters of any new technology always pay a price premium.

As things currently stand, if you have regular Wi-Fi access then given the patchy nature of 4G coverage, the price premium, and the fact that a much better 4G variant (the full-fat, non LTE version which is incompatible with LTE hardware) is on the way, it's wise to take a good hard look at whether you really need to commit to 4G at the present time or whether you're just doing so to try and impress others.

You'll only get definitive answers by asking your network provider.