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You can remove delegation (i.e. undelegate) by delegating exactly 0 Hive Power to the user you want to undelegate on.

Basic URL string (to put on your web browser URL box):
https://hivesigner.com/sign/delegateVestingShares?delegator=YOURUSERNAME&delegatee=DELEGATEEUSERNAME&vesting_shares=DELEGATIONAMOUNT

Replace "YOURUSERNAME" with your username
Replace"DELEGATEEUSERNAME" with the username of the account you are delegating to (or removing delegation from)
Replace "DELEGATIONAMOUNT" with the amount of Hive Power (HP) you want to delegate, using only digits (enter "0" to undelegate)

For example, to undelegate from me, use the string https://hivesigner.com/sign/delegateVestingShares?delegator=rubenbitcoin&delegatee=anonymouser&vesting_shares=0

The quoted text came from https://busy.org/@carlgnash/how-to-delegate-hive-power-using-hivesigner-com-url-string-parameters

Or simply go to your Hive wallet using PeakD @ https://peakd.com/@rubenbitcoin/wallet and click "Delegate". Enter 0 (zero) Hive Power Amount on the user to cancel your delegation to their account.