Can not update to lollipop due to TWRP recovery
You can either upgrade to L via TWRP itself (some reported having trouble with TWRP 2.8 and suggested trying 2.7) or revert from TWRP back to stock recovery if you want to go the OTA way (I guess that's what you're trying to do, you're not clear on that in your question).

Also instead of TWRP you can try ClockworkMod recovery.

edit: typo