Change dimensions of CNC layout

Hi all.
I am completely new to Librecad and just installed it today in order to change some dimensions of some dxf files I bought in order to make a camper van conversion in plywood. The files are great and show the the layout of how to cut each plywood boards, so it is easy to build afterwards.
However, the height of the whole unit should be a few centimeters shorter than the original, and so I would like to change the lenght of some of the lines.

I have attached a picture of one of the files and was wondering, if there is an easy way to change the lenght of the lines (where I put red arrows), since I want to shorten them 5 cm. And if i can make the long line (blue arrow) follow the lines

Maybe even both long lines (blue and pink) could follow (so the red arrow lines would be shortened 2,5 cm in each end), even though the other (pink arrow) is not straight.

Thank you!
Kind regards Mikkel

well, there are several ways to do this - and the most optimal way depends on the entity that was used in your drawing.

Are there several lines or just a single polyline?

Basicall, you may try to use something like this:

1) if the selection is for polyline - use "explode" command to split polyline to several lines. If they are individual lines - just skip this step.

2) horizontal lines (top and bottom) - use either a) "lengthen" command or b) modify "Entity's properties" or c) jsut move the line' endpoint grip by the mouse to the desired location

3) for vertical lines on the right - select them and move to updated position using "Move" command.

Together with proper snapping (say, to endpoints) - it will be quite an easy and fast operation, but probably not too obviuous for the first time use ;)

Yet with some practice I'm sure you'll be able to manage your drawings very efficiently...

Thx! Your explantion was really helpful for a first time user and saved me loads of time :) It works with the explode command to break them into separate lines, and can see that it is 1:1 regarding centimeters which makes it easy to adjust I hope.

Thanks for taking the time to reply.

You may also play with the "Stretch" command (Tools - Modify - Stretch). You can shorten / lengthen several elements in one go and don't have to explode polylines.

yes, you're right - stretch command will work too, yet it requires caution and preciseness if it's necessary to keep specific dimensions, so I suppose a bit larger yet safer operation will work.

BTW - I forget to mention that as soon as all coordinates are updated, it's possible to restore polylines using "Polyline From Segments" command.