You delete old photo attachments by clicking the drop-down menu by your profile pic on the top right corner of the page. The second option should be My Attachments.Click on that, and you should be shown all the photos you’ve uploaded. You have to click on the link next to each photo and delete them individually by editing them out of the comment they were posted in.
It’s time consuming, so I would suggest doing as said above, and using an image hosting service. I myself use Post Images because it’s so simple, but any safe site should work.
Most people post photos that are many times larger than needed and use up their space only because the file sizes are massive. Images can be changed in a few seconds in paint by reducing size in stretch. You can check the file size before and after and save under a different name to test. Most images can go from 3MB to 300K without losing resolution others could see (they are often out of focus at 3MB and wouldn't lose visible details at 30K).