cannot uninstall\update realmedia splitter

[BSPeter]

First rerun Codecmanager.exe (you can find it inside BS.Player's installation folder.)
Now, if you click on the line "Real Media Splitter" codecmanager will tell you in the box below the "Information/Description"-tab where this splitter is installed. (If the spitter is installed both "system" and "local" it will reveal this info for both installations. (You may have to scroll down using the handle at the right hand side.))
The actual filter's filename is RealMediaSplitter.ax. It can be installed (=registered) or uninstalled like any other "ax" filter. Unfortunately you didn't mention your PC's OS. If you google on uninstalling or unregistering ax filters (or dll filters for that matter) you will no doubt be able to find the answer for your OS.

In fact to uninstall/unregister, you may also use BS.Player's in-built "filter manager". (Note this is a different 'beastie' from the separate codecmanager.exe used before.)
Start-up BS.Player; then right click on it and select Options > Preferences > "Filter management". Now select the tab "Filter manager".
It will show all filters/codecs installed on your system. Scroll down (the list is alphabetical) and Select "RealMedia Splitter" (If shown more than once: in the box below the location of the selected filter is shown.) Now click on the button [Unregister filter] in the right hand column.