|If you have a multi-size pattern, here's an easy way to grade it up to the next larger size, or down to the next smaller size. (I'll describe it for grading up, since that's what I'm most familiar with!) I won't guarantee that this will be perfect, but it's a good place to start when your frustrated with patterns that aren't quite your size.
First, trace the largest size, let's say size 20. Then, place the traced line on the next smaller size (size 18), and trace the larger size again. This will give you a size (22) that is the same amount larger all around as the difference between the existing sizes (18 and 20). This also works with darts and other markings.
You'll need to move the tracing around as you go from side to side and bottom to top, and there may be some places where you just have to use your intuition to fill in the boundaries.