If you have win 7 you can install win 8 because it is considered an upgrade. Using that same method to go back to Win 7 takes a couple extra steps.

Win 7 comes with a couple of different versions. It has a 1st update pack so download that if you need it. This will save you time if you have the space on a USB Flash drive to store it. You can always download it later or purchase a version of Win 7 that comes with it.

Backup any files you want to keep. Once you start they will be gone forever. For instance if you have say some favorites in a browser or an address book try to export that info and save it on a flash drive. If you have any special settings for hooking up to the Internet like your ISP info you may want to save it. If you are using a router that info is probably in the router. However, you may be using special settings in your e-mail or something like that.

If you have a new Win 7 OEM version or a retail version that might be possible to install Win 7. I recommend that you do a install as if you were building a new computer. You want to insert the install DVD and then let it go to the first screen. You may need to pick an advanced install. First delete the partition and select to use all the space on the hard drive to create a new partion. This rewrites or forces a rewrite of all the data on the hard drive. You will then need to format the drive. These two first steps gets rid of all of the effects of Win 8, and gives you a clean slate on which to install a new OS of your choice. So then the program should automatically go to installing Win 7. If you can get to this part then it should install almost automatically. It may ask a few questions like language, Time Zone, etc.

I do not usually install software on retail computers. There are some problems that may pop up if you try this so I always suggest you go to your manufacturers support website first to see if anyone else is doing this. You may need chipset drivers or video and networking drivers to make it work.