Hi nchappell, Welcome to Dell community.You might be able to install windows 8 on your computer however Dell has not tested Windows 8 on this model and also the drivers are not available on Dell site for Windows 8. You may want to download the Windows 8 upgrade assistant to check your system compatibility from the below mentioned Microsoft site.[URL]
Will A Dell Optiplex 755 support Windows8?
OS Question For Windows 8