If I am not mistaken you have to install 64bit version for Java to use more than 1gb. As for how to do the rest they have a tutorial to help with allocating more ram here.
http://tiny.cc/ComplexRAM
I played on this server for a week and then reported myself a week ago for IRL deals not knowing that they weren't allowed ( was reporting a scammer and ended up banned x.x ), and during this time of covid-19 waiting for things feels as though time is running much more slowly. One week of...
In order to be unbanned from the server, you will need to create a ban appeal.
https://www.mc-complex.com/forums/pixelmon/form/ban-appeal.2/select
Waiting for someone to view mine at the moment, and it can take around two weeks. Good luck with your appeal.