You can upgrade to business class on Etihad by using the online process. You need to follow the steps for the Etihad business class upgrade as per described below:

Visit the official website of Etihad Airlines.
Click on the Manage option available at the top of the page.
Now tap on the choose your seat option.
It will take you to the next page, and you will reverse your seat option. Click on that option.
Fill out the Booking Reference Number and last name in the given boxes.
Select the Find my Bookings option.
Now upgrade to business class on the flight of your choice.
Etihad Airlines will send you the confirmation message on your registered email.

How can I upgrade my business class for free?

If you want to upgrade to the business class, then under the conditions, you can do that for free. The following conditions are mentioned below:

If you have existing Etihad guest miles, you can use them for the free upgrade.
If you are a premium member of Etihad Airlines, then you can upgrade to business class.
Sometimes airlines upgrade your traveling class to business class if available. So you can contact them about the availability.

Can I upgrade to business class after online check-in?

Yes, you are eligible to upgrade to business class after an online check-in, provided you have made the reservation through an online process and seats are available. If there are some charges, you must pay for the upgrade.

Can I upgrade my seat to business class at the airport?

Yes, you can upgrade the seat to business class at the airport. It depends on the availability of the seats. You need to speak to the customer service representative about that. If there are seats, then they will upgrade it to business class.