How to change my local airports mesh?

Hi all,I have been flying around my local airport and I have noticed some big errors in the mesh. By errors, I mean that there are big ditches at the side of the runway etc...Would someone please be able to tell me which tools I will need and what files I need to create so that I can make these changes? I have never done mesh scenery for msfs, which is about the only thing I haven't done so far so any help would be much appreciated.Kind regards