Upgrade from Home to Proffessional

I have purchased a laptop with Windows 7 Home, but I have a genuine dvd and license for Windows 7 Proffessionsl.

I am looking for any tips, pointers or warnings before I go ahead and install Professionsal over Home.

I am hoping it will offer an upgarde option take the new license andd go ahead and install the additional features, leaving everything else (existing software, data, etc) neatly intact. But any advise regarding this would be gratefully received by the Winbdows 7 newbie.

Maybe I missed it but can't quite see anything that fits this scenario. I am told by the retailer I can do it, but they did seem in a hurry to say this and anything to enhance my confidence before proceding with what might not be reversable would be appreciated.