1. Backup your current WTF and Interface folders.
2. Download and extract Gliff UI to your desktop.
3. Go into the the GLiff UI WTF folder, enter the "Account" folder and rename "YOURACCOUNTNAME" to your own account name in all caps. (This needs to be your account name, not your battle.net account name)
4. Enter the "YOURACCOUNTNAME" folder and rename "YourServerName" to your server's name (Capitalize first letter).
5. Enter the "YourServerName" folder and rename "YourCharacterName" to your character's name (Capitalize first letter).
6. Put the Gliff UI WTF and Interface folders into your World of Warcraft folder. (Do not forget to backup your WTF and Interface folders before this point)
7. Once logged in, make sure you have "Load out of date Addons" checked.
8. Once logged in, type "/reflux switch Gliff UI"
9. Type "/ec". Go into the "ElvUI AddonSkins" option and uncheck Omen, Skada, Quartz.
All credit goes to the individual addon authors.
Please do not forget to backup any UI you had before installing Gliff UI. I am not responsible for lost data during the installation.