I encountered this error message when trying to update
a record in the SQL Server 6.5

Error message: Incorrect syntax near '='

My SQL statement is:
Update tablename SET qty = qty + 20 FROM tablename
where Rtrim(LTrim(Order_no)) = '12345' AND
RTrim(LTrim(sku_no)) = '11111'

Anything wrong with this statement? Pls help, thanks.