How to downgrade Windows 7 Ultimate To Home Premium

[boosters]

I am using Win 7 Trial version which is now going to be end. I recently purchased Win 7 Home Premium. I want to know how should i downgrade to HP. I can't format my pc because there is lots of files i downloaded and i don't have much space to store all those files, also don't have external HDD.

So please someone suggest me a solution

[Ponmayilal]

Please go through this article very very carefully. Read it, and reread it as many times as it would take you to understand the full implications and then decide whether you want to do it.

IMO, the best thing you could do is to backup all your data and do a clean install. Personally I would not go for any other convoluted solution with attendant risks.