In The Legend of Zelda: Skyward Sword for the Wii, you can upgrade the shields in the game at the Scrap Shop by collecting various items throughout the world.
Here are the shield upgrades, and what you need to collect to upgrade them.
Banded Shield – Upgraded from: Wooden Shield, Cost: 30 Rupees, Ingredients: 2 Amber Relics, 1 Jelly Blob, 1 Monster Claw
Braced Shield – Upgraded From: Banded Shield, Cost: 50 Rupees, Ingredients: 2 Monster Claws, 3 Amber Relics, 1 Ornament Skull, 2 Tumbleweeds
Reinforced Shield – Upgraded From: Iron Shield, Cost: 50 Rupees, Ingredients: 2 Eldin Ores, 2 Monster Claws, 2 Ornament Skulls
Fortified Shield – Upgraded From: Reinforced Shield, Cost: 100 Rupees, Ingredients: 1 Blue Bird Feather, 3 Eldin Ores, 3 Monster Claws, 3 Tumbleweeds
Divine Shield – Upgraded From: Sacred Shield, Cost: 100 Rupees, Ingredients: 2 Bird Feathers, 1 Dusk Relic, 3 Ornament Skulls
Goddess Shield – Upgraded From: Divine Shield, Cost: 150 Rupees, Ingredients: 3 Bird Feathers, 1 Blue Bird Feather, 4 Dusk Relics, 3 Monster Horns
Check out my full upgrade guide if you’re looking for the other upgrades for equipment, potions, and wallets.