Katie,
If you changed pics directly on eBay, they don't sync back to update the SG or the Store image. That you'd have to change by uploading a replacement, i.e. use the Replace button with Image selected (box at left) on the Image Management page. If you are just hitting the button without selecting and not uploading, that's not actually doing a Replace. Replace includes an UPLOAD of image, just like original upload.
Updates to Title do sync back, i.e. it's a periodic update done by Auctiva.
Hope that helps.
Danno