I need to change shape object

frequently i changed shape in object but
whenever i change shape i have to make it from scratch.
is it possible to change shape or appearance already Push&Pulled model? not make from scratch?
i marked yellow line on the attached picture which for example change to shape .
and also how to draw long height circle like width is 3mm and height is 6mm long.
i want to know what is best and efficient option.
thanks so much

dddd.stl (24.1 KB)

Upload the SKP file instead of the STL.

You should be able to draw the new curves and use Push/Pull to push away the waste.

Untitled.skp (2.4 MB)
hi i uploaded!

In your model the thing is 2D so you should be able to just draw the new curves and erase what you don’t want. If you want to modify it after the thing is 3D, do what I said, above.

You should purge unused stuff from your models. I did on yours and reduced the file size to less than 3% of what you uploaded.

thanks so much i learnt much!