Hi Randomgu,
To assist you better I would appreciate if you could answer the following question:
What is the make and model number of the Computer?
I would suggest you to run the Upgrade Assistant before upgrading to Windows 8 Operating System.
Upgrade Assistant checks your PC hardware to see if it meets the Windows 8 system requirements to install on your PC, including features of the processor such as CPU speed, PAE, NX, and SSE2, as well as RAM size and hard drive capacity.
It also checks for compatibility of your currently installed apps and devices.
Regarding how to install Windows 8 Operating System;
Step 1:
I would suggest you to check and make sure the computer meet all the requirements for installing Windows 8 Operating System;
Windows 8 system requirements
http://windows.microsoft.com/en-IN/windows-8/system-requirements
Step 2:
If the computer meets the system requirements for Windows 8 Operating System then, I would suggest you to run the Upgrade advisor and then attempt to install windows
Refer to the section “Download Upgrade Assistant” from the link;
Upgrade to Windows 8
http://windows.microsoft.com/en-IN/windows-8/upgrade-to-windows-8
How to upgrade to Windows 8
Refer to the section “Install Windows 8”
from the link;
http://windows.microsoft.com/en-IN/windows-8/install#1TC=t1
Regarding how to install Windows 7 Operating System;
If you want to install windows 7 Operating System, first I would suggest you to check the System Requirements for Windows 7 and make sure the computer is compatible to Windows 7 Operating System;
Windows 7 system requirements
http://windows.microsoft.com/en-us/windows7/products/system-requirements
Installing and reinstalling Windows 7
http://windows.microsoft.com/en-US/Windows7/Installing-and-reinstalling-Windows-7
Installing Windows 7: frequently asked questions
http://windows.microsoft.com/en-US/Windows7/Installing-Windows-7-frequently-asked-questions
Refer to the link;
Upgrading from Windows XP to Windows 7
http://windows.microsoft.com/en-in/windows7/help/upgrading-from-windows-xp-to-windows-7#T1=tab01
If you need further assistance regarding Windows, please feel free to post. We will be happy to help you.