I have changed my Hotmail username and want MakeUseOf notification email to be sent to my present email address.
You can't. You can add and remove connections to other social networks for an existing account, but if you login with one hotmail account then you can't just replace it with another random hotmail account.
If it's still using the SAME account/ID, but you've migrated from say a @hotmail.com to an @outlook.com address, then it should automatically update the notification email address for you.
It depends which MakeUseOf notifications you are referring to.
I'm guessing that you are subscribed to our newsletter. If you want to change this email address, please unsubscribe form the newsletter with the old email address. There is an unsubscribe link at the bottom of every email.
To receive the newsletter under your new address, you need to re-subscribe. Please enter your email address in the respective field in the sidebar on the right and click the red Subscribe button.
If you are referring to comment notifications or the rewards program, you have to log in with a different account, i.e. your new Hotmail account.