First, shutdown your PC and remove the mains plug, unplug the keyboard (remember which socket) and hold it upside down to release any debris from in-between the keys (pressing the keys is a good way to release it). If you have a can of compressed air then use it to blow any debris from around and under the keys, if not, then use the hose of a vacuum cleaner to remove it. All the keys can be removed although the larger keys (space bar, enter key, shift keys, backspace, caps lock, etc) can be difficult to put back. Therefore, you might avoid removing them.