Most of my patterns are in scale 1:10 based on the metric system, but it is not hard to enlarge them. The most easy way is to use a paper with a grid. In the description below I am using paper without grid.
Scale 1:10 means that each mm in the booklet corresponds to one cm in reality. Observe that the in pictures below the difference is less than 1:10 for readability reasons.
Take the piece you want to enlarge and start at a straight corner (draw one if needed, otherwise one of the corners of the paper is normally good enough). Measure the height of the piece – use a ruler or measuring tape, measure number of mm in the booklet and draw them as cm on the paper. Sometimes it is useful to draw a short line for each 10cm as a base.
Then you measure the width of the piece at the corner – measure in mm in the booklet and in cm on the paper – and mark on the paper. Measure the width at the next important point – typically at a corner or where a curve starts. Now you can draw the straight line between the points.
Now we come to the part of the pattern where the line curves and we have more details, then we want to measure the width at each of the 10cm lines. In some cases we also want to add extra lines based on the pattern. In this case we want the width where the shoulder line meets the curve for the armhole.
With all the points we have it is now easy to draw the curves too. Also draw possible marks, in this case a line for the waist.
Now you are ready and can cut out the pattern.
For pieces without clear straight corners it is easiest to start with a cross in the grid, even if it is positioned outside of the piece. From this cross you can start with positioning the corners of the piece. Then continue as above, but measure the distances between the vertical line and both sides of the piece instead of only one side.