Thanks guys. Heres the answer. I Completely forgot about the case clause.
UPDATE Salaries
SET Salary =
CASE
WHEN (Salary between 30000 and 40000) THEN Salary + 50000
WHEN (Salary between 40000 and 55000) THEN Salary + 70000
WHEN (Salary between 55000 and 65000) THEN Salary + 90000
END