I need to make it so IntelliJ idea uses less ram, any tips to make it use less ram?
Be aware that all IDEs tend to demand much RAM. This includes IntelliJ, NetBeans, and Eclipse. They are not intended to be run on machines with constrained resources.
IntelliJ by default has many active plugins.
Use the Plugins panel in preferences to examine each one. Deactivate the ones of no use to you.
FYI, if the computer in front of you is constrained but you have access to a more powerful computer remotely, you may want to try the JetBrains Client to make use of IntelliJ running remotely on that other machine. See the JetBrains page, Remote Development Overview.
I vaguely recall that JetBrains announced a paid service where they would provide an IntelliJ environment in the cloud. You could configure to your liking, paying for CPU cores and memory. I don’t know the current status.