Gearing change on Mongoose Malus I recently purchased a Mongoose Malus, I would like to change out the front gear so I have a true granny gear (ie really low gear) and am not concerned with the top end speed.

Where can I purchase and what is recommended and how difficult will this be? This bike is mostly used around the ranch at very slow speeds in sand, grass, gravel and rocky areas mostly not even on a path.
I can't find a clearly written spec page for this bike, but based on the picture your easiest change will be to swap out the cassette/freewheel for a 7 speed with a larger number of teeth. 

The question is whether the rear derailleur can fit a larger gear. 

You'll also need a new chain to add more links.

Your other option is to replace the whole front chainring assembly with a smaller one.   At this price point there's a good chance its a common square taper fitment, so you might even be able to rescue a smaller crank off a donor-bike.

You could even use a triple crank off a MTB but only hook the chain onto the middle or little ring.   This would be the most economical option, the only bike-specific tool you need is a crank puller.