When accessing my profile there is no functionality to change my avatar. When I first accessed my account the functionality was there; now, it is gone.
I am assuming that you are using cloud. In cloud you have to make the change in your Atlassian account, you can find information in the document at the bottom of the page. https://confluence.atlassian.com/jirasoftwarecloud/managing-your-user-profile-764478256.html
If you are using server you can get instructions here: https://confluence.atlassian.com/jirasoftwareserver/managing-your-user-profile-939938953.html
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