League Managers are able to add Bench and IR/IL slots post-draft (no removing slots once added) to their league's Roster setting. This applies to Bench and IR/IL slots only—all other position slots remain locked (no adding or removing).
To Add/Remove a Bench or IR Roster Slot (LM Only / Web Only)
Click on LM Tools
Click on Edit Roster Settings under Roster Tools
Scroll down to Bench and IR/IL and adjust the number as desired
Click on Save Changes