The server guide does not show how the JVM options can be set.
It sould be in chapter "1 Getting started" or "16. Troubleshooting" and link to the other

There are several options to set JVM parameter
By environment

• GC_LOG=Y|n  a flag whether to switch off gc logging
•  JAVA_OPTS  override the default settings within the server.con (GC_LOG still set if not disabled)

by edit the bin/server.conf

• Overwrite the default "-Xms64m -Xmx512m -XX:MetaspaceSize=64M"
• Uncomment examples, i.e. "remote socket debugging"
• Or add additional settings to the end "JAVA_OPTS=$JAVA_OTPS ......"