What do you intend to do with the quilt after you redesign the pattern. Why do you need to give credit. Is the quilt to be entered into a show. Did the original look like an original design. If you look at quilts in magazines you might notice that few if any are truly original but just rearrangement of traditional patterns.
Just changing size does not free one from copyright laws. Even the myth of "changing 30%" does not free one. If yours looks like or can be recognized from the original the design is still under compyright. I know this from experience. I talked with a copyright attorney about simple shapes and was told rearrangement of simple shapes does not violate. A classic case a few years ago related to the "Dear Jane" quilt. Someone made one and posted it on ebay for sale and used the name "Dear Jane". Author of the Dear Jane book sued because that name is copyrighted. It was reposted on ebay under the name "in the style of Jane Stickle quilt" which was the original antique quilt.
Go to:
http://www.how-to-quilt.com/sylvia.php and then search for Sylvia Landsman who has written extensively about copyright in the needlework industry. The above site is about a conversation with Sylvia.