Changing Theme For Custom WP Setup

Hi,

So I have a WP site, where I hired a dev to redesign the homepage. What she did was create a child theme of existing one and then used some plugins and some custom php code to redesign it.

It is ok but Im having a feeling she did cause some issues with the site which has affected several things such as speed.

What I wanted to ask was if i just go to Appearance>Theme and changed the theme to a new simple fast loading one, would that be ok?

Would I be able to switch back to the current one without causing any issues if i didnt like the new one?

I know you can do it normally but this is a modified child theme, thats my concern.

Thanks

The page I need help with: [log in to see the link]