Ah, this classic issue. You're going to want to take a tool for leverage (my favorite is a butter knife) and gently unclip the left and right side of the space-bar key. Once you've done this be careful of the metal springs or tiny rods. Don't lose them! Then clean the area by either scraping with something like a flat-head screwdriver or using a little cleaner (making sure to not get it inside the keyboard). Then place the rods/springs back carefully placing the key back at the same time (they have to be aligned). I've cleaned many keyboards.
Good luck! Ask me any more questions or voice concerns.