Great question! Sizing up shouldn't be too difficult, really... it's all math! I would recommend determining the finished measurements you want the bodice to be first.
Let's say you want it to measure 28"... and the gauge is 4.5 stitches to the inch. So 28 inches x 4.5 st/inch = 126 stitches. Which means 63 would be for the front bodice and 63 for the back. The skirt in this pattern has twice as many stitches as the total bodice... so 126 x 2 = 252. You would use 252 stitches for the skirt, decrease to 126 for the bodice, divide in half to 63 for the front and 63 for the back.
The only other small changes you'd need to make are figuring out the number of stitches for the neck vs shoulders (but you could figure out the percentage they used on the smaller size, and apply that percentage to your total bodice stitches) and the length of the bodice overall, and length to the armhole shaping.
I'd say go for it. I hope this was helpful!