So, I basically just slashed the block (minus the seam allowances) and spread it the desired amount. I was looking for a pretty neat, non poufy fit so spread the pattern to the width of my measurements(ish) at the hip. Because the woven is cut on the bias there is some stretch in it, so the fit is comfortable.
I increased the width of my pattern by a total of 4cm on the front and 8cm on the back (pictured below is half this measurement because it is only one half of the garment). On the back I spread in a couple of areas to help retain the leg shaping.
I also increased the length of the pattern by 2cm.
These measurements are only a guide as you will need to measure your pattern and yourself to see how much you need to increase, but this clearly shows the method.

Mark a new diagonal grainline to cut on the bias and smooth out the lines. The crotch piece remains unchanged!
Because the pattern you are using may differ in the amount of ease included you will have to measure up and maybe make a trial run or two to check the fit, but I hope this helps!
Have a good weekend! x
P.S. Here are some links to some pretty great free knickers patterns!
Woven mini brief which could easily be adapted for more coverage from the secrets of sewing lingerie book. You do have to register your email and name, but you don't have to revive junk emails.
http://www.lovesewingmag.co.uk/free-sewing-patterns/item/520-knickers-sewing-pattern
Another excellent pattern is sozo's free jersey knicker pattern download. So generous and there's even a vest!
http://sozowhatdoyouknow.blogspot.co.uk/p/free-patterns.html
P.S. Here are some links to some pretty great free knickers patterns!
Woven mini brief which could easily be adapted for more coverage from the secrets of sewing lingerie book. You do have to register your email and name, but you don't have to revive junk emails.
http://www.lovesewingmag.co.uk/free-sewing-patterns/item/520-knickers-sewing-pattern
Another excellent pattern is sozo's free jersey knicker pattern download. So generous and there's even a vest!
http://sozowhatdoyouknow.blogspot.co.uk/p/free-patterns.html