Hi,
You have to do quite a few things to address to fix this issue.
First thing is to stop WordPress from generating unwanted image so it doesn’t pile up again in the future. Second is to remove the already existing generated image sizes.
Note: Before you do anything, We suggest you create a backup incase anything goes wrong.
For the first part, you can use a plugin that removes any unused media image sizes from your site.
You can try using Force Regenerate Thumbnails plugin.
For the second part, you’ll have use a plugin that cleans up your media library for any unused media files.
You can try using Media Cleaner – Clean & Optimize Space plugin.
Let us know if this works for you.