Help on themes for a complete starter!

Hi there,

1st forgive the naieveity here but I am about to try do my own website for my business but know very little, having done some reasearch on domains, hosting etc I am trying to get my head around themes, which one to pick.

For most of the themes for for eg https://www.freewpthemes.net are they tweakable/customizable, lets say for instance the below theme suited the look I wanted but my businesses colour is red, is it possible/easy to switch the yellow to red. See link:

https://www.freewpthemes.net/preview/predilection/

Or are the free themes all what you see is what you get and only thing you can do is insert your copy?? Sorry for the stupid question,

Regards,

Gary