Select Case error "Incorrect syntax near = "

I can never seem to get case statements right.  Object of game,
If PPS.intStage_Number % 2 is even then leave the Proc_Pkg_ID as it is
If PPS.intStage_Number % 2 is odd then increment the Proc_Pkg_ID by 1

I’m getting the error  Incorrect syntax near ‘=’ on the line PP.Proc_Pkg_ID =
I need a hand with getting the syntax right


Declare @CurrStageNo int
Declare @NextStageNo int
Declare @StageResult int


--Testing-----------------------
Declare @Proj_ID int
Declare @Val varchar(20)
--------------------------------
set @Proj_ID = 2
set @Val = '1400270182RS'


SELECT    
      PI.Proj_Item_ID,
      PP.Proc_Pkg_ID =
            case PPS.intStage_Number
            when PPS.intStage_Number % 2 = 0 then PP.Proc_Pkg_ID + 1
            else PP.Proc_Pkg_ID
            end
      FROM    tbl_Projects_PackagesStage PPS
                  INNER JOIN tbl_Process_Packages PP ON PPS.Proc_Pkg_ID = PP.Proc_Pkg_ID
                  INNER JOIN tbl_Package_Stages PPS ON PPS.ProcPkg_Stage_ID = PPS.ProcPkg_Stage_ID
                  INNER JOIN tbl_Projects_Information PI ON PPS.Proj_Item_ID = PI.Proj_Item_ID
      Where
            PI.Proj_ID = @Proj_ID
            AND PI.sItem_Number = @Val
            AND PPIST.bActive = 1
            Order by PPS.intStage_Number Desc