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