Move a keyframe in time only

Hi,

I'm in the Animation Editor and I'm trying to move my keyframes. I want to shorten the animation by moving the ending keyframes a few frames back in the animation. The problem is this: when I drag the keyframes, they move in both time AND space. I'm changing the valuse of the keyframes and I don't want to. Is there a way to lock the keyframe editing to just time?

Sorry if this question has been asked before. I looked several times, but maybe I'm using wrong keywords... Thanks for the help!