You do NOT MUST to, SyncToy 2.1 support upgrade installation.
For further details info please go to link
http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=c26efa36-98e0-4ee9-a7c5-98d0592d8c52 .
Pieces info for upgrade:
Upgrade:- If upgrading from an earlier version of SyncToy (e.g. SyncToy 1.4 or SyncToy 2.0), it is
**CRITICAL** to ensure that all folder pairs are fully synchronized using the previous version before running SyncToy 2.1 setup. Not following this guideline can lead to unintended behavior and partial data loss when running SyncToy 2.1 for the first time after upgrade. All folder pairs must also be fully synchronized at least once right after the upgrade is done.
Thanks,
Ping
This posting is provided "AS IS" with no warranties, and confers no rights.