You definitely should ensure there are Win7 drivers for your computer before doing anything else. Some Mfr's haven't done that, and might not. So check.
Assuming that's all done, then backup every file you want to keep. I assume you have all the program-disks for their complete reinstallation, too, yes? That's important.
Then just wipe out the hard-drive and install a new copy of Win7-whatever.
One other note... laptop hard-drives are relatively cheap - $50-100. I'd consider buying a new HDD with my Win7 purchase, then removing the existing Win8x hard drive, stick in the new one and install Win7. That way, in case something didn't work, I'd have my original hard-drive intact.