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This is a somewhat significant upgrade because the 2.2 branch was a different from anything else.
What modules do you use now and what versions of php and mysql are you using on your server?
You will want to shoot for 2.5.4 as your upgrade path but you will want to try this upgrade on a computer separate from your Live host.
Chances are that unless you are well versed in php and mysql that this will be a tough task. You are best off trying to pay someone to convert for you depending on what modules you are using and how big your site is. Your other option is to start a new site from scratch.
But let us know what you currently have installed and we can go from there. How many users do you have and is it a busy site?
Attending College working towards Bachelors in Software Engineering and Network Security.