You are logged on to the database as a database user.
The current database user created the synonym.
The database is in the ONLINE operational state.
Select the synonym in the explorer tree.
In the context menu of the synonym, choose Definition.
In the context menu of the editor window, choose Edit.
Change the name of the synonym.
In the context menu of the editor window, choose Alter Synonym.
SQL Reference Manual, RENAME SYNONYM Statement (rename_synonym_statement)