Recommended approach is to use LogoManager plugin. It has simple user interface, configurable from MediaPortal itself, has logo autoupdate function, and allows to select different logo templates (called "desings" there).
If LogoManager does not support logo pack for your country, then you have the possibility to get all logos manually:
First you need to download the required images. Good sources are:
After you have downloaded or created the required logos, you need to put them in the correct folder for MediaPortal to find them.
First find the Team MediaPortal application data folder.
Tip: Start Menu; Programs; Team MediaPortal; MediaPortal; User Files
Inside this folder, there is a folder
\Thumbs\TV\Logos where you put your TV logos, and
MediaPortal\Thumbs\Radio for radio logos.
To make MediaPortal show the correct logos, you have to match the image filename to the corresponding channel name.
If you performed all previous steps, and MediaPortal still displays your old logos, then this is because of the cache. MP uses a cache to quicker load graphics and other resources, but a side-effect of this is that changes to the graphics files will not be immediately visible in MediaPortal. Clear the cache by closing down MP, and deleting the MediaPortal\Cache folder. After you restart MP, you will now be able to view the updated logos.