Cleaning the mirror is a pretty big deal, not to be undertaken lightly. A little dirt won't hurt the operation of the telescope much.

You might try getting a small can of compressed air from a photography shop and blowing the dust off.

The important thing is not to try to wipe the dust off a dry mirror.

For an very dirty mirror, you'll have to disassemble the telescope, get the mirror out, clean it gently with detergent and water, re-assemble, then re-align.