Unfortunately, there's not an easy way to modify the size of a C2C crochet graph pattern unless you're the original designer. Your best bet for making a larger blanket is choosing a thicker yarn (category 5 weight or higher) and the appropriate size hook. This will make each C2C tile you crochet larger, which will create a bigger blanket overall. Similarly, to make a smaller blanket, use thinner yarn (category 3 weight or lighter) and a smaller hook.