In order to remove a Video CODEC, you must first know what that CODEC is called. In this example we wish to remove a Video CODEC that we downloaded from the internet called "Angel Potion", since it is being used to decompress our files, when we actually wish another Video CODEC to do the job. Therefore, I have made to decision to remove it from my computer.
Then you should see this below window open.
Double click on "Multimedia" to see your Multimedia Properties. Then you should be the below window. Across the top there are five tabs ("Audio", "Video", "MIDI", "CD Music" and "Devices"). Click on the "Devices" tab. Then double-click on the "Video Compression Codecs" item, and a list of all the Video CODECs you have on your computer should expand under it. In the below image I have selected the Video CODEC I wish to remove, labeled "AngelPotion [DivX ;-) High]". After I have removed this one, I will remove all the other Video CODECs that begin with "AngelPotion..."
Now that you have the CODEC highlighted, you should be able to click on the "Properties" button and the lower right of the window. This should then display the properties of that particular CODEC as seen in the image below.
Click on the "Remove" button and confirm you wish to remove it, but selecting "Yes".
The device will now have been removed, and you will see this message confirming it.
Click "OK".
Click "OK".