Double Drawn Lines

when selecting lines inside a sketch, anything inside the selection box when cresating it to the right , selects only those lines inside the box - create the box to the left and it selects anything it crosses.

if you window select the double line, the property tab will list both. right click on the one you want KEEP in the list and delete it from that  list. you now only have the other one selected, and can just hit the delete key.

RMB, select other, then pick an entity in the pop up selection box that comes up.  Or if you know where the lines you want start and stop, and I assume their points are different than the rectangle, drag a window starting from the left side to the right side, over and containing what you want to delete.  If only the line you want to delete is in your window, dragging a window from left to right will grab only this line.  Dragging from right to left selects all entities in the dragged window.

You can right click on the line and select "select other", gives the option to select you want.