WP.com is not an image management platform. Image files are stored in your media library as you upload them.
I've never used the editing wp.com provides, probably because I started my first blog before they had that feature.
When I've tried it on test blogs for answering questions here in these forums, it was not a very good image editing platform either.
My blog is about cooking so small images are often useful but when they are uploaded as large files wp.com does a ratty job of displaying them (though okay for my purposes.)
But displaying small pictures doesn't necessarily mean the files are small. You really have to take care of compressing your files before uploading.
I started looking at image sizes on your blog, but then got distracted by reading it. The most recent pictures didn't look like they were outrageously huge. Are you running out of storage space?
When I first started blogging some of my files were 300 or 400kb but I quickly learned that an image under 100 kb, even under 50kb look just fine online.
But the bad news is that there is no automatic way to compress your image files. If you resort to compressing them and reloading them you'll have to also re-insert them into your posts and pages because they will be renamed.