Hi there, this video will show you how - https://www.youtube.com/watch?v=Ouk5-LU9LEY Marry Christmas
Remove the crumb trays and scrub. Shake out all extras crumbs. If you have any stainless on it I used Goof Off with amazing results. It might work on other material too. It wiped away old gunk that tends to build up on them.
There isn't much you can do to the inside except for cleaning up the crumb tray. You could put paper towel around a table knife and possibly get to some parts of the inner walls, but be careful to not damage any thing. When you empty the crumb tray, make sure to shake it a bit to get any higher up bits, I also give it a few taps to try to loosen things further. Make sure you unplug it before you do anything!
Hi Mar: First of all, and you know this, unplug your toaster. Over the sink, open the crumb tray on the bottom and wipe it clean. Shake the toaster to remove any crumbs that are hiding inside, and if you see any crumbs that are in reach, but not behind the heating elements, you can wipe them out with a toothbrush. The outer covering can be cleaned with vinegar or soap and water, but don't put the toaster in water, only wipe it off. Sometimes, if the ick is bad on the outside, a magic eraser will work wonders. Toasters don't need a lot of attention, just shaking out and the crumb tray cleaned. Good luck.