Welcome!
When stationary, Hub Lock button first, then either H4 button for high range 4wd, or shift from 4H to 4L on the shift lever for low range 4wd. I've never driven on soft sand, so I can't really comment on whether you'll need high or low range, but my guess would be low range if its...
I sometimes have trouble uploading photos as well. I find it works best to just drop them into the message box than to use the upload tool.
Cruiser looks great though!