IF EXISTS (
    SELECT 1 FROM INFORMATION_SCHEMA.ROUTINES
    WHERE ROUTINE_NAME = 'fn_MyFunction' 
    AND ROUTINE_SCHEMA = 'dbo'
    AND ROUTINE_TYPE = 'FUNCTION'
) 
BEGIN
    DROP FUNCTION dbo.fn_MyFunction
    PRINT 'Dropped dbo.fn_MyFunction'
END

TSQL delete function if it already exists

SQL