screwed my mac over probably

I added bootcamp a couple years ago and since then havent be able to update my mac b/c it takes up too much space. I ignored it cause it didnt cause a problem but my computer is getting slow asf. Now im trying to remove bootcamp but i need more storage to remove it and I dont even know what to do. Please help! I have a storage disk I can plug in if it may help though I dont know how to use it. https://preview.redd.it/fkum9jkjuw7e1.png?width=542&format=png&auto=webp&s=00e18db00d291dead12ae4583e77684ee7554abb