Unstaking delegated stake from one’s own node works in precisely the same way as a third party unstakes. “Owner” stakers may use the Desktop Wallet just like any other token holder and unstake tokens from their validator. The same delay of 500 epochs is in place for network security (approximately between 1 - 3 weeks depending on how quickly the network is producing “rounds”).
If a validator node unregisters their node, this doesn’t take effect until the end of the current epoch. This is because all validator set changes happen at the epoch switchover - when the Radix Protocol selects a new validator set. A validator is expected to correctly participate in consensus through the end of the epoch during which they requested unregistration. After this, the Radix Public Network will no longer consider the node for inclusion in the validator set, regardless of the amount of stake delegated to it.
To issue the command to unregister, the validator node operator creates a special unregister transaction from their node’s address. More details on this can be found in the Radix Technical Documentation.