This is how I sharpen my hedge trimmer. Two things first: Make sure the bolts that hold the trimmer parts together are reasonably tight, don't overdo it. Use some 20 or 30 weight oil to lightly lube between the moving parts. After putting on the oil, restart the trimmer to spread the oil. Wipe off the excess. Sharpening: a hand file, relatively of the smooth variety. If you can place the trimmer in a vise, that would be helpful. File each cutting edge at the same angle as was done by the manufacturer - you can tell by the brighter surface that has been exposed by the filing. You may have to move the blade a little to get to all of the surfaces by starting and restarting the trimmer. Do not sharpen or trim fingers.

I do like Fruitjarfl does, except I use a Dremel tool
instead of a file. My blades/teeth are curved on my
Crapsman trimmer. I use the chainsaw sharpening stone
in the Dremel.