Completing wiping Lightroom clean

Hello,

my Lightroom is jsut a mess and now that I've properly started my Lightroom I'd honestly just like to wipe it clean and start completely fresh! 
all photos I need i will save securely obviously.

how would I go about/ do this ?? 

Also will it effect anything too much ? Or any photos saved on my computer ? 

I would love to know it's driving me mad ... I've recently change from windows to Mac and when opening Lightroom it is trying to sync thousands and thousands of images and idk where these are coming from ... obviously that cache/catalog but struggling to find them all on Mac ...