Factory reset dell laptop

[virajqs]

Now we can upgrade windows 7 to windows 10.
https://www.microsoft.com/en-us/windows/windows-10-upgrade

My laptop is dell xps l502x.I had activated genuine windows 7 with it.But with the introduction of windows 8.1, i installed windows 8.1 which is a patched version(Not genuine).Now i want to go back to windows 7 in order to get the free upgrading to windows 10.
I have the dell backup cd with me.
How to get back to windows 7 without loosing my data on other two partitions.
Because in the past,one time i tried doing it and lost all my data on other two partitions.

 

[u_make_me_sick_]

Back up ur data, create an additional partition and transfer ur important data to that partition, then install win 7 in C drive.