How do I increase the amount of ram my 1.12.2 modded minecraft server is allowed to use?

[Plapypie]

I'm hosting a forge server for RL Craft (1.12.2) on my own personal computer and its sort of slow and when I check the server it says its using around 900 Megabytes of ram and there is 0% free, however I have 16 gigs of ram total and task manager says around 30% to 40% of it is free. So how do I allow my server to use more ram? Is there a way to increase the amount of ram its allowed to use? Also here's a link to a screenshot of what the server looks like when its running I hope this helps: https://drive.google.com/file/d/1ogCsRcNy_eEIan1E2cJt9efrfn5bfOPD/view?usp=sharing

[LexManos]

1.12 is no longer supported on this forum.

Please update to a modern version of Minecraft to receive support.