I currently have Windows 8. The computer is used mainly for The Microsoft Flight Simulator. From the opinion of many simmers Windows 7 is better. They claim there are certain issues with Windows 8 that could cause problems. I have a Windows 7 Home Premium disc. right here on my shelve. How difficult would it be to change my operating system ? I have a WD External Hard Drive, would I have to do something with that? Thanks in advance