Tuning Garbage Collection in Apache Tomcat

I have the following parameters in tomcat6.conf

JAVA_OPTS="-server -Xmx6144m -Xms3072m -XX:+UseConcMarkSweepGC -XX:MaxGCPauseMillis=999 -XX:ReservedCodeCacheSize=128m -XX:MaxPermSize=256m -Djava.awt.headless=true -Dcom.sun.management.jmxremote=true -Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.authenticate=false -Djava.rmi.server.hostname= -Djava.rmi.server.useLocalHostname=false" 

but at peak time I see the following regularly,

ERROR memory-watcher - used 87.73865761212004%, max 6403194880 reaping at priority CRITICAL

is there any parameter I can use to to tune tomcat performance or GC ?

Brother Printer printing garbage after upgrade to 18.04

I have been using the Brother MFC-J6935DW printer, for almost a year, with Ubuntu 16.04 over wifi. Worked like a charm.
Yesterday, I upgraded to Ubuntu 18.04. Most things went off pretty well. The only challenge I have not been able to resolve is that the printer starts spewing out garbage after the first couple of lines.
The things I have tried are:
a. Reinstall printer
b. Download the driver from the brother site and reinstall that.
c. sudo apt-get install lib32z1 lib32ncurses5 lib32stdc++6 (as suggested on another thread here).
d. Reinstalled Ms fonts
e. Upgraded to the latest firmware.

No luck as yet. Any suggestions, please?
The only workaround I have at the moment is to print the pdf document as an image (I really need to get this resolved before my wife needs to use the printer!).

Attached is an image of what I get when I try to print a standard document.

Remove garbage from Media/jw with command line

While running f3write erroneously at first I left some garbage files in my Media/jw directory – 1.h2w and 2.h2w. How do I get rid of them?

I can find them with the GUI but I don’t have permission to remove anything there by deleting or dragging them to the trashcan.

With the command line I don’t know how to get to that location in order to use sudo.

How do I cd above the Home directory using the command line?