How to change site geo-location in google serps ?

I bought a .net domain, which used to be hosted in UK. I transformed this site to my topic and moved it to US based hosting / IP. Google still thinks it's based in UK, my USA google rankings suffer. What else can i do ?

If you want to dominate local listings, you can observe how Google lists those business in your local region. Then duplicate their method of success + do it better.

I have several sites all hosted in US but each of these individual sites are still able to have great results in their respective regions like HK, JP or US.

Most of the time, I use the "observing" technique, in which I observe sites which rank well for Local Serps, then I duplicate but I get more aggressive and do it better...

OP was asking about regular search results and not Local listings. I think there are a few ways in which Google decides a website's country specific rankings. The address mentioned in the 'contact us page', the TLD domain if applicable, and the server location.
Since you have already made these changes, I would suggest you to log-in to your Google Webmaster account and set US as your preferred target audience country.

How long has the transfer been in effect? I had a similar situation with a .CA domain that does a lot of business in the US. We're still using the .CA, but we bought a similar .COM and did a redirect into the new .COM to kind of start fresh.

It took about 4-6 weeks, but after that the rankings started to shift to be more US based.

Also, do what beazt said and change this setting in Google Webmaster Tools, that should help out a bit.

Other than that, I'd also question what type of backlinks and such you already have. Are they from UK sites, or from US sites? That could also have an effect.

Tnx for the suggestions !!.

I've already set webmaster tools to US (by default google showed UK), will also add contact page with some US based address, links i add are 80% from us based sites.

Yes, I just wanted to suggest, that try to implement Webmaster tools. You can just implement it for a short time and if you start to do hardcore SEO, then take it back off.

I use WT from google.

One more question. What if i get country specific TLD like .im and i want it to rank in Google.com for USA ? Will IP address and seting my target audience to united states in webmaster tools do the trick ?