I'm thinking to replace my legal Windows 7 OS with my cracked Windows 8.1 copy. The thing is that I have 4 partitions that this PC have since I have it Do I need to delete all those partitions to install W8.1 or just the C: one? I don't really want to lose the Recovery partition since I can use that to reinstall W7 and I don't know what's the purpose of the E: one.
No need to delete the recovery partition. Win 8 will only add a 300 MB partition (bootsector and stuff) to the setup. BTW: No need to 'crack' anything, recommend using proper activation .
So I just format the C: partition and install the W8.1 there? And I'm gonna active the W8.1 using KMS activator
As i don't trust that recovery partitions, i recommend doing a full image backup with Acronis True Image or similiar, just to be safe. But that's at least your choice .