Go to Members (main navigation) > Manage members (dropdown)

Click on any member's name or profile image to go to their profile page.

Click on the blue pencil action button in the action button bar at the top right of the page, below the main navigation.

You will now be able to update any of the text content in the fields displayed. Click the tick at the bottom of the page to save any changes.

To update a profile image, click the blue pencil action button that is overlayed on the profile image. If you are editing the text fields, you will also see a blue image action button in the action button bar which will also activate the image uploader. 

Once you have uploaded and sized the image, click the tick to save.