This has been asked many times before and the answer already is in the ERAS user guide.
From the ERAS User Guide:
-Personal Statements can be edited at any point during the application season-
even when assigned to programs that have been applied to.
- Personal Statements that have been edited will be reflected on the programsí side
by an updated status containing the date of the updated version but programs
are not guaranteed to view or review updated versions of Personal Statements.
So yes you can edit your personal statement anytime during the season and it is updated automatically on the program's side BUT the programs are not guaranteed to view the edited version.