Changing customized them to a new one.

Wondering if anyone has the time to give me some feedback.
I need to change this wordpress site: https://www.thesensus.com/ to this new customized theme ( https://easysite.by/?theme=teardrop ).
Will this be nightmare? Can you recommend any tutorials for this? I can work with HTML/CSS but I do not know php.

Thanks for any input you can offer!