I Need To Upgrade The OS of My PC

It has been some months that I am planning to upgrade the Operating System or OS of my pc. It has a Windows XP with SP2 operating system. The SP3 is still waiting to be upgraded. I am just scared to lost some important files, data or documents in my pc one I will upgrade it to SP3. I will wait until my new notebook will come next week so that I can change the OS to SP3. I just want to make it sure before I do it. I have been planning to do it couple of months ago but life online and offline is always busy! more updates to come later!