Try unplugging it and cleaning all the crumbs out of it either through the slot on the bottom if there is a clean-out or through the top by shaking it vigorously. You might want to do it outside or at least over the garbage since there will be a lot of crumbs and it will be hard to control where they land as they fly out.
Beyond that, if you can take the cover off, use a sponge or an old tooth brush to clean off the release mechanism, which in your case seems like it's sticking.
Perhaps spray a shot of electrical contact cleaner on the moving parts to keep them free to move throughout the rest of the life of your toaster.
Plug it back in and work it up and down a few times before you toast any bread. After that, toast it up and enjoy those eggos!