Just to be clear the A1470 is the last model Time Capsule and is Gen5. Apple refer to it as AC model.
Replacing the disk is certainly possible.. although the construction of the Gen5 makes it rather a chore.
See the ifixit article on replacement of the disk.
https://www.ifixit.com/Guide/Airport+Time+Capsule+A1470+Hard+Drive+Replacement/61924
IMHO the task they rate as moderate is actually difficult. The sockets on the board are surface mount and easy to damage. The ribbon cable to the hard disk is easy to tear. Do not take on the task lightly.
If the TC is 4years old or more it might really be better to replace it.
Anyway you can certainly replace with any size drive.. NOT SMR type. Look it up as it is important.
Typically a NAS drive will suit fine. And you can use sizes up to 8TB as I have done it myself. Over 8TB is also likely fine but I see little point to it.
Note the mountings of the hard disk will need re-fabrication because they only fit that model seagate. It is purely friction fit with rubber wedges .. no screws at all.