What the server gets
Your plan's RAM is the container limit. Our start command uses -XX:MaxRAMPercentage=95 (Paper, Forge, NeoForge) or -XmxM (Fabric), so the JVM may use almost all of it, and the rest is headroom for the process itself. You do not need to set anything.
Can I change the start command?
The command itself is set by the server type and is not editable in the panel. That keeps the memory settings consistent with what you bought. What you can change are the variables in the Startup tab (version, jar name, loader version). If you want tuned garbage-collector settings ("Aikar's flags") on a busy Paper server, open a ticket and we set them for your server; they help most above 20 players.
More RAM is not always faster
A server that has more heap than it needs spends longer in garbage collection pauses. 4 GB for 10 players on Paper is generous; 16 GB for the same server is not better, sometimes worse. Modpacks are the exception: they genuinely need it.