The fastest and easiest way isn't always the best, but if you want to try it to see, you can leave the layout as it is and save the InDesign document, then make an 8x8 document and place the original doc into the new one the way you place graphic images. After the small page is placed on the larger one, you can fit the image to the new size. If the old page is 7x7 like you say in the body of your post, it will scale proportionally to 8x8 at around 114.25%, but if the old page is 7.5x8 like you say in the thread's title, it will scale to around 106.5% on the shorter edge, and you will have to decide if it looks good enough out-of-proportion.
That's the easy way, but maybe not the best. You will also have to keep the original to make edits and print from the new one.
Liquid layout rules take a little time to figure out, but that is how you scale the page elements up (or down) to accommodate a new page size. While they were designed for digital publishing, they will work great for you in this situation.
Here are two recent articles explaining how this works from one of my favorite InDesign gurus—Erica Gamet. She presented Liquid Layouts for my user group in Denver—everyone benefited tremendously.
Take a look: