For example - the EvaDress 1940s Swing Trousers 3322:
Darted at the waist:
The same pattern, without waist darts:
1. To remove the darts, trace around your pattern piece (we never cut the original, right?)
2. Redraw the dart lines down to the side edge of the pattern piece, somewhere near the knee area. Keep the same start points on the waist edge.
3. Fold the new dart closed.
4. Retrace your new pattern piece, and re-draw the waist so it's even (you can see the faint blue line of where the previous folded piece was).
And that's it! Front darts gone and your new pants pattern is ready to be made into jeans.
I hope this tutorial helps if anyone was wondering how to do it :)