It's 10, 20 for the second one ~Nathan Drake said:For a bigger wallet, kill gold skulltulas, go the skulltula house in Kakariko Village (sorry for misspellings if there are any, it has been a LOOOOONG time), and I think it's once you hit about 20, they should give you the first wallet upgrade.
Edit: 20 for the Shard of Agony, 30 for the second wallet upgrade