Gather 4 ancient debris for 1 netherite tool upgrade
Smelt ancient debris in a furnace to get netherite scrap
Combine 4 netherite scrap with 1 gold ingot in a crafting table to get 1 netherite ingot
Obtain the base tool you want to upgrade (diamond pickaxe, axe, shovel, hoe, or sword)
Open a smithing table
Place the diamond tool in the left slot
Place the netherite ingot in the right slot
Take the resulting netherite tool from the output slot