How do I change my IP address from UK to USA to play Combat Arms NA?

I need to change the IP (proxy) to US, but i must be able to change it back again to UK (I play Combat Arms in EU servers, want to try the US, but don't want to do it permanently, so there must be a way to switch between US and EU IP [and back again]). There are software utilities which do that for you, but you need to pay for their services, and i don't know how to do it for free...

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