How to Upgrade Vanilla Netherite Gear to Netherite-Diamond
Prepare the smithing table
Smithing_transform is the recipe type used for gear upgrades. Place a smithing table, open it, and put your existing vanilla Netherite item in the base slot. The template slot and addition slot take the materials the transform expects — for the Netherite-Diamond tier, that means a Netherite-Diamond Ingot.
Upgrade each piece
Apply the transform to a Netherite Helmet, Chestplate, Leggings, and Boots to get Netherite-Diamond Helmet, Netherite-Diamond Chestplate, Netherite-Diamond Leggings, and Netherite-Diamond Boots. The same transform works on tools and weapons: Netherite Sword, Pickaxe, Axe, Shovel, Hoe, and Spear each become their Netherite-Diamond counterpart.
Choose your tier
You are not locked into Diamond. The same smithing_transform path exists for Netherite-Emerald, Netherite-Gold, and Netherite-Iron gear. Swap the addition material to the matching upgraded ingot (Netherite-Emerald Ingot, Netherite-Gold Ingot, Netherite-Iron Ingot) and the vanilla Netherite piece becomes that tier's version.
Plan the order
Upgrade the pieces you use most first — usually the Chestplate and Pickaxe. Each upgrade consumes one upgraded ingot, so count your stock before starting a full set. If you are short, craft more ingots at the smithing table before you begin.