Quit Steam completely
Open Finder
Go to Applications
Drag Steam to the Trash
Open Finder
Click Go in the menu bar
Select Go to Folder
Enter `~/Library/Application Support/Steam`
Delete the Steam folder
Go to `~/Library/Preferences`
Delete `com.valvesoftware.steam.plist`
Go to `~/Library/Caches`
Delete any Steam-related cache files
Go to `~/Library/Logs`
Delete any Steam-related log files
Empty the Trash
Restart your Mac