demo template theme vs child theme

Hi,

After I got my demo template (Highend Presentation) installed I have started to make changes and working on my site on demo template version. Is this a wrong approach? Should I create a child version of demo and work in that or is it ok to make changes on demo template version? Will this create problems with future updates?

Another question: I’m unable to make changes on title/subtitle fonts on demo version.(trying to change the weight of the font) It appears that highend theme options don’t control these changes. It must be done in css somewhere on the demo template but Im unable to locate it?!

Also, Im unable to locate how to change background picture (Screen shot attached) on Highend presentation theme About us page (world map image) ,header video on Contact page ,and background image on Our Services Page at the bottom over which numbers and icons are placed.

Your help would be much appreciated
Many thanks
Stefan