The Girls' Coachella Shorts were just re-released and have been lengthened just a bit, but if you would like to add additional length -- follow along this post.
I would suggest that you only lengthen the pattern a max of 1-2" since the leg holes will remain the same size and may be too wide if lengthening too much. But feel free to lengthen as you wish of course!
First, you'll want to print off two sets of pattern pieces (or trace a set).
Lay a piece of paper under one of the front pattern pieces and tape it to the paper.
Measure the inseam and decide how much you will be adding. I'm measuring 2" here (this total includes seam allowances and is not the finished inseam measurement). I will add 1" for a total inseam on the pattern piece of 3".
Lay the second front pattern piece you have printed or traced, on top of the taped down piece.
Slide the pattern piece down so that the inseam will now be the length you would like. Tape in place.
Next, cut around the pattern piece, using the rise/crotch curve of the pattern piece that is taped in place, following the new inseam, and the curve of the pattern piece that is laid on top.
Now we will repeat the same process for the back piece. Tape the back down on a couple pieces of paper and lay the second back piece on top.
Slide the pattern piece straight down and measure the total inseam you decided on. Tape in place.
Draw your new piece, cut out and you are ready to sew these up!