Ok - no problem.
Below is a simple shape with a simple "Motion Path" converted to keyframes (white arrow).
Clicking the icon under the blue arrow will reveal the keyframe editor.
With the keyframed object selected in the layers list, click the icon under the green arrow [Transform Keyframes Tool]. (The colored lines under the yellow arrow show the original keyframe set before editing.)
Click and drag a selection around ALL the visible keyframes. A white framed rectangle with drag control points at the corners and midpoints will appear (see under orange arrow.) Click and drag the MIDPOINT on the right side and drag out to the time you you need. All the keyframes will be adjusted "linearly" and evenly throughout the range of the time expansion or compression.
Note: You can use the Transform Keyframes Tool to control selected keyframe points without affecting unselected points. You can also click inside the Transform Keyframes Tool and drag the selected points to new locations, thus keeping portions of an animation intact with respect to each other.
HTH