When renaming a Fund, any existing transaction with that Fund selected will be updated with the new Fund name.  If you wish to keep the old Fund name on those transactions, you would want to create a new Fund rather than renaming the existing Fund since the new name will eliminate that old Fund name entirely.  To rename a Fund:

1. Click Management
2. Select Funds beneath Donation Strategies
3. Click on the name of the fund you want to change
4. Type the new name for that fund in the Name field
5. Click Save and View all Funds