Most people don’t, for natural reasons, correspond to the standard sizes S/M/L. Sometimes it is good enough to take the next larger size but when the fit is important you may need to adjust your enlarged pattern to your measurements.
Adjust Bottom Length and Width
In most cases you just need to add or remove the wanted number of cm at the bottom of the front and back pieces. The same accounts for the gores, even if the width below will be changes. If you don’t want to change the width you can adjust the angle of the gores. This is something you can do anyhow, to increase or reduce the bottom width without changing the length.
Adjust Bodice Length
You increase the bodice length by cutting the front and back pieces apart from side to side, between the waist and the bottom of the armhole. Then you pull the pieces apart as much as you need to lengthen the bodice and tape them onto a strip of paper.
If you instead want to reduce the bodice length, you cut as above, lay the pieces with the needed overlap and tape them together. In both cases slanting or curved lines, in case the side seam may be slanting, need to be adjusted to make them even.
Adjust Sleeve Length
You adjust the sleeve length by cutting it apart from side to side in the middle and pull apart or lay with an overlap as above. The sleeve seam normally needs to be adjusted to make the curve/slant even again.
Adjust Bodice Width
You increase the bodice width on your garment by cutting the pattern halves of the front and back pieces apart from top to bottom, pull the pieces apart as much as is needed and tape with a paper strip in between. You need to pull each piece apart one fourth of the increase you want. If you e.g. need to add 4cm to the breast width, you add 1cm to each pattern piece.
If you instead want to make the bodice narrower, you cut apart, lay the pieces with an overlap (one fourth of the want reduction) and tape together. If the shoulder seam is slanted it will need to be adjusted to an even slant in both cases.
Adjust the Width of S-shaped Sleeves
S-shaped sleeves are slightly more complicated to adjust. If you only need to change up to a cm it is good enough to cut and change the width in one place in the middle. If you need to change more it is better to cut and change the width in two place to ensure that the s-curve looks good after the change too.
When you pull apart or lay the pieces with an overlap you can do that as much at the top as at the bottom, as in the pictures above, or you can change more in one end than in the other, depending on where you need the increase or reduction.
When you have changed the width of the sleeve at the top you need to adjust the armhole so that it still fits. Cut the front and back pieces apart from side to side at the middle of the curve for the armhole. For each cm you change on the sleeve you need to adjust half a cm on each of the back and front pieces. When you do this, the bodice length will also be changed. If you want the standard bodice length you need to change it back by adjusting the length, as described above under Adjust Bodice Length, in the opposite direction.