It would be of great help if you could post a pic of the muffler on your saw, as there are a few different muffler designs used on 028's.
The idea behind a muffler modification is to increase air flow. The first step in doing this is to remove the spark arrestor/catalytic converter. Check your local laws before removing the spark arrestor, as it's against the law in some parts of the world to operate a chainsaw without one.
After the spark arrestor and baffle are removed, reinstall the muffler, and retune the carburetor. If you are not happy with the saw's performance, you will have to increase the size of the opening on your muffler. Depending upon what style muffler your saw has, this can be done with something like a Dremel tool.
If you want to get fancy with your muffler mod, you can add either a second opening to the muffler, or add a short pipe to the current one. (Or both.)
Be careful not to over-mod the muffler, if you do, the saw will be way to loud to operate comfortably. I've read on this site that the surface area of muffler opening(s) should be about 85%-90% of the surface area of the exhaust port on your saw's engine. This will provide maximum performance while keeping the noise relatively low.
One way to measure the area of the engine exhaust port is with spaghetti, make sure the piston is at top-dead-center, and put spaghetti lengthways into the exhaust port until no more will fit. Count the noodles, subtract 10% and mod the muffler until the 90% of spaghetti will fit into the opening(s) of the muffler.
Hope this helps!
