Hi Carsten from Bavaria,
There are various ways but this is the easiest:
You start by selecting all the objects whose keyframes you want to move. Then execute the command “BongoMoveKeyframe” at the command prompt. Click the Object option.
“Start of tick range” in your case I think will be 0 and “End of thick range” the far most right keyframe you want to move. “Distance in ticks” allows you to move the keyframes either back or forth.
Negative ticks are not an option.