tactics trainer

How do I change to a different tag? I seem to be stuck on "mate in one". I have tried to select different tags but no change. 

The "mate in one" thing is a kind of button that becomes a menu when you click on it, called a "combo box."  If you click it, you should be presented with a menu listing lots of different choices.  Pick something, and you should get a pop-up menu, such as, "Are you sure you want to suggest the tag 'Mate in 3+?"  Click OK, and there you go.

Thanks, I was doing exactly that but somehow it was not working out. Although it worked for me yesterday. 

How come Chess.com uses the word "suggest" instead of "select"? It sounds ambivalent. Shouldn't a choice be selected? 

Because what you're doing is making a suggestion for what the tag should be.  After you make the suggestion, I'm not sure what the next person to view the problem will see.  It might appear like any other tag, or it might say "suggested" beside it or something.

One way or another, all tags are subject to a voting process.  There are little thumbs up and thumbs down icons beside each one, and after some number of down votes, the offending tags are removed by the system.  It might be that tags show "suggested" until they receive some number of up votes.  I've never seen that, and just don't know.