Hmmm. If I remember correctly, it's easy enough to change it from 2 to 1 columns. But It won't change the width of the skill window. So the cursor box will extend the entire length of the skill window, rather than half.
And I'm pretty sure the MP cost is right-justified while the skill name is left-justified, so there will probably be a large gap between them.
So what you're asking for might not look so good.
Edit: So just goto Window_Skill in Scripts. Change @column_max from 2 to 1.
But it'll look like this. The cursor extends the length of the window, but there's all this empty space on the left.
edit 2:
So if you go down to Draw Item. And add 160 to the x value, That'll nudge everything over to the center of the screen.
These three lines draw the skill icon, the skill name, and the skill cost.
and you'll get this: