I would like to know how to increase the maximum amount of units that can be simultaneously on the battlefield. I tried google but it said i should edit the xml file and that i would have to download it but i don't know how to implement it into the game files. can anyone help me?

Yes :)

If you download from http://empireatwar.filefront.com/file/FOC_XMLs (this link is not longer working, but that was were I downloaded it years ago.....)
But I found another one

http://www.gamemaps.com/details/1205

Download this file, extract it into SWOC\data folder

Or even better

Create a new folder in mods (i.e. mymod), extract it into there and to start this mod

Just create a empty text file

Insert just this line (by using notepad or similar, BUT NOT wordpad, word or whatever)

swfoc LANGUAGE=ENGLISH MODPATH=Mods\mymod

(in case you want to use English, if not replace with any supported language)

Once you saved this line, rename the file into (i.e.) mymod.bat
To start the game just doubleclick on this bat-file. place for the bat file i.e. D:\GOGGames\Star Wars - Empire At War Gold\EAWX

This will make sure that the running version will not be corrupted.

Now the big question:

Battelfield meaning land battle or space battles?

Space battles is much easier ( you just have to change the population limit in the appropriate faction file)
Land battle, you would also need to change the maps involved as there is a limit per reinforment point as well.
It would not make much sense sayign 30 units, if the map itself would restrict you to 4 units ;)
And going above 10 land-units will crash the game in strategic mode when zooming in onto the planet....
Space a lot of mods are using much higher numbers.

I cant seem to get it to work, the bat file to launch the mod D: