Here are the steps I use to make sure I'm seeing the largest version of the image available:
1. Click on the thumbnail of the image on the main photobucket page. This will go to a new page on the website.
2. Hover mouse pointer over image...If it says less than 100% (seen in black box in upper right corner of image), click on image again. This will go to the page within Photobucket with the full size image.
3. Right click and save as....
If the image is at 100%, this is as large as it will be..