To upgrade the golem, craft the upgrades and apply them in anvil. Upgrade can provide modifiers to golems, which adds special abilities or improve stats. Golem can only have limited upgrades, and each modifier has its own max level.
Use grindstone to remove all golem upgrades. Blast golem holder item with explosion to retrieve upgrades.If you have Create installed, you can use deployer to automatically apply upgrades without experience cost.