I'm using Word Perfect 12 Microsoft Mode.

I'm typing a paper. Originally, I double-spaced the lines. Later, I
single-spaced some other lines.
Now I want to close up the double-space lines but the blinking cursor
won't go between them, or if I backspace a line it won't close up to the
line above it.
Is there any way to close up the double-space lines, which seem to be
subject to computer mind control?