Scratch

Umm are the games your own or semeone else's?
If they're not yours, then there's no way to remove them,  you can only ask the owner to do it (him/her)self.
But if they are yours, there's an easy way you can delete the games from the gallery.
Step 1. When you go the "My Stuff" page, you'll see all your projects listed there. Each project has a little "square" next to it. Click on that square to  "choose" or "select" the project. When you do that, a check appears in the square to let you know which project you marked.
Step 2. As soon as you marked all the projects you want to delete from your gallery, look at the top of the screen and search for the button "remove from gallery". Click there and you'll see a list of all the galleries which you own or have subscribed to. Choose your gallery (again, by clicking on the square) and press "ok" at the bottom of the list. Now you have removed the projects from your gallery!