Hi guys,
I just want to share this information with you because I've tried to find how to do it for a long time. Actually, it is like taking candy from a baby.
Firstly go to https://peakd.com/ and login with your Hive account. You will see your Hive power and delegate button in your wallet.
Just click on 'delegate' and fill the required information (Delegatee account and Hive power amount).
I hope it helps!