Helping people with computers... one answer at a time.
There are lots of media players with varying capabilities, strengths and weaknesses. Even if you don't like Windows Media Player you'll need something.
How do you delete a program as default? I wish to take Windows Media Player off as default. It does not handle half the extensions as some other players.
By "default" I'm going to assume that you mean the default for playing a media file when you double click on it.
It is possible to remove the associations, but honestly, I don't think that's what you really want. Removing the association leaves you with no program to be the default.
Instead, you want to replace the default program with the one of your choosing. Doing that by hand can be difficult, but many programs have a shortcut that makes it pretty easy.
I happen to use VLC media player, a free, open source, cross platform media player that supports many, many different file types and encodings. I'll use it as an example.
When you run the VLC Setup program, one of the steps allows you to choose various options for the install:
I've scrolled the list of options down somewhat to uncover the File type associations options. I've selected all (you can expand the lists to examine the list of file types in more detail, and to pick and choose if you like) and on completion the setup program will register VLC media player as the default program to play all those file types.
That's by far the fastest way to set up "something else" as your default media player when you double click or otherwise open a file. No "unregistering", no deleting, no having to figure out what file types you care about, just let the setup program do it.
Most other media players do something similar, either at setup time - often in the "Advanced" or other non-default options selections - or as an option in the program's preferences dialog.
In fact, Windows Media Player itself has a similar selection as part of it's options:
If you decide you want Windows Media Player to play some, or even all, of your media files once again you can simply run it and return to this options dialog.
Almost every other approach involves manually setting the media player for each individual file type that you care about. If you're looking to make a wholesale change, as it sounds like you are, using the replacement utilities ability to set it all up for you is most likely the best way to go.