Edit the batch file that you launch the server with. Notepad works for that. Just edit the file, and you'll see two sets of numbers in it. Those numbers set memory, just have both of them set to the same value. Just be sure that you don't allocate more than your system can handle. Like if you have 4 GB of memory total, don't go and allocated more than maybe 2.0 to 2.5 GB.
Nothing in that guide makes sense. And what batch file? I can't find any batch file. Just that jar file and a bunch of other text files. I tried using a text edit, but it's not working the same. It' still gibberish and I can't change the text format.
I made the server for you, so to speak. Just unzip the folder, and there you have it. If it doesn't run, then you need to set up the path variable, if you haven't already. There are instructions for that on the wiki page I gave.