You cannot get the Hoodie upgrade until you have a security clearance of 5 or higher. You can get a security clearance of 5 by collecting the Party Pass and then do Monty Golf or Fazer Blast. Another option is to do the Loading Dock or Prize Counter mission, whichever one you skipped when Freddy first gave you the option. Once you have a security clearance of 5 go to the Monty Golf lobby in the Atrium. 

Look to the right of the Monty Golf elevator and you will see stairs going to the second floor. Take these up and go left around the corner, here you will find a long hallway. Go towards the large door at the end of the hall but do not go through it. On the other side will be a bunch of security bots, so before we go through we want to hop in Freddy.

Now you can go through the door and you will see a bakery and several security bots around. Enter the bakery and go forwards towards the large cupcake in the wall. To the left of it is a doorway, and in this next room you will find another security bot patrolling in front of a blue door. This door can only be opened if your security clearance is 5 or higher.

Go through the blue door and go to the corner of the room so the door closes. You must be careful not to accidentally open the door or the security bot will grab you. On top of the toilet will be a present with the Hoodie upgrade inside. After getting it you should hop back in Freddy and return to exploring the Pizzaplex.