You can use the head cleaning sheet that came with it - if you can find it! Or, just put a length of fairly stiff rough surfaced paper with some alcohol on through the machine. The labels last a long time but tend to loose their stickiness.
When we had lots of these printers I got adept at taking the heads off to clean but it is fiddly and the dot matrix head is sharp - I have cuts to the fingers to prove it. I now use Zebra label printers and print everything from Word, the later Dymos can only be used with DYmo labels an I wanted a size they dont do.