Daedalus:
After downloading and installing the Daedalus wallet client, use the wallet restoration functionality to restore your Byron-era wallet and move it to a new Shelley-era wallet. You’ll need to enter the wallet recovery phrase associated with the Byron-era wallet. You’ll also need to write down the 24 word recovery phrase for your new Shelley-era wallet and create a new spending password.
Once you create a Shelley-era wallet in Daedalus, you’ll gain access to the delegation center where you can view stakepools and make your decisions on which pools to delegate to.
Once you find the list of stake pool in the delegation center section of Daedalus, click on the stakepool to which you would like to delegate and then click the button “Delegate to this pool”.