More image size woes

Hey all. I’ve searched high and low, or maybe just my version of high and low, and haven’t seemed to find my issue addressed.

I’m trying to control the max image size on the main page, right now it goes to full size.

Then when you click on the actual blog post it’s full size (which I don’t mind). Clicking on the image gives me a weird thumbnail size that is not the size I set in permalinks.

I’ve tried all sorts of different plugins, but they don’t seem to work. Almost like the Theme CSS is overriding any sort of plugin.

I’m using an older theme, that’s been modified over the years- Juyicyroo.

The blog address is weheartella.com if you would like to see.

Any help would be much appreciated and I’m happy to post any code or get more (or even less) specific, if need be.