If you still have the original project with the first four measure still intact, go back to it and when deleting the four measures, use Delete Special, and check "Delete Hole".
If you can't go back to that version or don't want to because you've made other changes since, the best method is probably to select all tracks and cut everything from the current starting point (From=Now) to the end (Thru=End), and then paste it at 1:01:000. Use Cut Special and Paste Special to make sure everything is included and the starting track is correct.
As always, use Save As, and modify the project name when saving after massive changes like this. Better yet, save to a new name
before you make the changes.