Starting with laser cutting acrylic, how to delete these unwanted lines?

[Mcffee]

Attachment 125372

I like to remove the overlapping lines that should not be cut by the laser. Tried different buttons (Xara Xtreme) and once managed to remove a part, but can't find back how I did it. The result should be like the right image but outlines only. I guess there is also a fast way to remove all the lines at ones but no idea how.

Thanks!