Method 1: Using CASE Statement

I believe this is going to be the most popular solution as we are all familiar with CASE Statement.

UPDATE SimpleTableSET Gender = CASE Gender WHEN 'male' THEN 'female' ELSE 'male' ENDGOSELECT *FROM SimpleTable
GO

Method 2: Using REPLACE  Function

I totally understand it is the not cleanest solution but it will for sure work in giving situation.

UPDATE SimpleTableSET Gender = REPLACE(('fe'+Gender),'fefe','')GOSELECT *FROM SimpleTable
GO

Method 3: Using IIF in SQL Server 2012

If you are using SQL Server 2012 you can use IIF and get the same effect as CASE statement.

UPDATE SimpleTableSET Gender = IIF(Gender = 'male', 'female', 'male')GOSELECT *FROM SimpleTable
GO