How to Manually Install New Cinnamon Themes (Linux Mint/Ubuntu)

To manually install new themes for cinnamon from the page provided by Cinnamon Settings, first backup the data of the original theme by opening a terminal and entering

sudo cp -R /usr/share/cinnamon/theme /usr/share/cinnamon/theme_backup

Then download and unpack another theme from http://cinnamon-spices.linuxmint.com/themes, save the files to some location - I will save them on my desktop.

Then you have to copy the data from the unpacked folder to the theme folder of cinnamon:

sudo cp -f /home/howtoforge/Desktop/unpackedfolder/cinnamon/* /usr/share/cinnamon/theme

The new data has then replaced the old. To restore the default theme, copy back the backed up data.