Apple consider it a sealed consumable.. it is not openable.. fixable in any way.
Well Apple are not always right. You can open it, and install a larger drive.
If under warranty.. that is void.. obviously... although working carefully whose to know.
If you are filling drives in a month.. even a 3TB will be full in 3 months.. this is going to be an expensive exercise.. I would recommend you mod the TC and use external sata port.. so you can swap hard drives regularly.
What A1xxx model is your TC?
You need to realise that not all TC take all drives.. and there are issues with some brands.. ie put a WD 3TB green in a Gen 2 TC it might work.. (it might not) make sure you are on latest firmware. It probably won't spin down.. but might.. and might not.
2TB tend to be easier to use. Good luck.