Completing wiping Lightroom clean

[#1]

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 ...  

[#2]

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 ...  

[#3]

Which version of Lightroom are you using? You post this in the Lightroom Classic forum. If you are indeed using Lightroom Classic then apparently you have enabled sync for the catalog and now Lightroom Classic downloads every photo you've got in the cloud.