Delete a Note in MuseScore2

Welcome, click it->Del it should work.

Voice 1 rests cannot get deleted (you don't delete silence), voice 2-3 rests and notes can get deleted by selecting them and press Del. Deleting notes will replace music with silence, AKA rests.
If you want to delete notes/rests in a manner similar to deleting characters in a word, use cut and paste

As mentioned, to delete a note, simply click it and press Delete. This removes the note and leaves all other notes in exactly the same time position as when you originally entered them. If in fact you want to move some number of subsequent notes earlier, just do that directly. No need to even start by deleting anything, although it doesn't hurt. just select the notes you want move earlier, cut, click where you want them moved, paste.

But if you want to "delete" a rest from voice 1, you can make it invisible. Select rest/rests and press V. Press again to make it visible again. Sometimes while making lead sheets I need to have "empty" measures or when you want to have some room for writing notes by hand. And there's also a menu option View->Show Invisible to get completely rid of visibility of invisible things on screen if wanted.