They are not easy to remove as the tarry substance you can see jams them in, you will probably need a proper extractor, these are available on ebay for less that it would cost you to have the job done:

http://www.ebay.co.uk/itm/9-Pc-Piece-Common-Rail-Diesel-Injector-Extractor-Puller-Bosch-Set-CDI-Mercedes-/270998740758?pt=UK_Hand_Tools_Equipment&hash=item3f18c89f16

There are some better ones that clamp on and extract using a screw thread which in very difficult cases are the only way of removing them.

In the mean time it would be advisible to change the oil as particles of carbon can get into it as a result of this problem which can lead to blocked oilways and turbo failure.