Hi Toonicorn,

To remove the bits you don't want you need to use the Shape Tool.

Briefly: Select the line you want to edit, go into the Shape Tool, move the pointer to the place where you want the line to end and the pointer shape will change to a white arrowhead. Click to create a new point in the line, then select all the other points on the line beyond your new point (using marquee selection) and delete them.

This becomes very easy and natural the more you do it. One of the the excellent community helpers here might be able to explain it better.

Phil