Before transferring your store to WooCart we might ask you to clean up the installation before we proceed. You can also do a clean up if you want to see if there's any performance available by removing unnecessary files.
Before optimizing, you want to know what you're dealing with. Go to Tools and click Site Health (available from WordPress 5.2).
And then click Directories and Sizes and you get a nice overview of your installation.
The two things you should be looking for is high disk usage in Uploads directory size and Database size.
The first one can be large if you have plugins saving a lot of files, large images, etc. Make sure you don't have any unnecessary files in there.
Database size is a bit more complicated but a large one can signal there are issues in the database.
For simple clean up you can run a free plugin like WP-Sweep or Advanced Database Cleaner. If you have a large database that might be a result of orphaned databases from old plugins, take a look at the pro version of the second plugin.
You need to do a manual review of files in the Uploads directory.