You should have two lines with the following content (at lines 25 and 42 more or less):
export JAVA_OPTS="-XX:MaxPermSize=512m -Xms256m -Xmx512m -Djava.awt.headless=true"
Just try with:
export JAVA_OPTS="-XX:MaxPermSize=1024m -Xms512m -Xmx1024m -Djava.awt.headless=true"
I hope it helps you. Please remember restart the server afterwards. Regards.