Inherited Design, Learning LibreCAD

Hello all.

I have inherited a product design in progress and it includes some DXF files for an enclosure with three metal parts. The enclosure is a PacTec P-8 with a rear panel, a top panel and an interior chassis for mounting PCBs.

I am a physicist by education who does embedded electronics hardware and with reluctance firmware.
Now I am trying to fill the role of mechanical engineer about 45 years since my junior high school drafting class.

Just starting with LibreCAD and learning how to open files and about layers and getting the drawings I inherited to print.  Other new users were also having difficulty with printing.
I started by down loading / installing the most recent version but found many more tutorials for the older user interface of version of 2.0.11 so I have changed to that version at least for the time being.

In the design I inherited, I also found lots of unused layers and layers with unrelated designs in them which I have deleted to remove clutter.

Next I need to learn how to change the size of a rectangular hole in the rear panel which was set up for a MINI TYPE B USB connector and change to standard size TYPE B connector. (From 0.35" x 0.25" to 0.5" x 0.45" )

While I am fluent with PCB design packages the conventions in the mechanical drawing world are another language to me.

I hope to also do hobby projects with LibreCAD as I have recently purchased (er, Santa is bringing) but not assembled a light duty CNC router.

I live in the Eastern Time zone in Tennessee and do amateur astronomy / astro photography as a hobby an with which I have used Arduino and Raspberry Pi single board computers.  

Forrest Erickson