To be fair if you enter the search term
change the level cap
into the "search this forum" box, you get this thread.
While this has been asked many times this forum has over 1500 threads and 17,000 posts. Regardless of that nobody has actually ever answered this particular question with any level of authority. The closest anyone came was "edit the "mapxx.exe" file and even then did not get into any kind of detail. All other answers provided were "use the forum search" which is totally unhelpful. If you don't know the answer either say nothing or simply say "I don't know". Nobody will think less of you for that.
-----------
I personally don't know where to edit the exe an really have no interest in doing so.
However most know that if you attempt to edit an exe file without knowing exactly what you are doing, you will completely screw up the executable. Few are willing to tell you how to do that because there are different versions of the map server exe file leaked out to the wild and not all will have the level values at the same offsets. That leaves you having to do your own decompiling of the map server with IDA to find its offsets and editing the exe file with a hex editor they are found.