What do I need to lookout for when redesigning website? I have 0 SEO experience

Hi everyone, I am new to SEO, have recently joined a startup as a co-founder, have been put in charge of rebranding the front-end of my application. Currently the page does have decent SEO I believe with backlinks etc, but besdies a couple of hours of reading, I'm totally new to SEO.

My question is how will a total brand redesign ie, changing of colors, assets, layout, possibly some copy (plan to keep site map the same), affect my current SEO rankings?

Also what would I need to be careful about when going through this brand redesign?

If there's any tools I should know of that you guys use often to help with SEO please let me know as well, would be greatly appreciated.