Step 1) Click on the profile that is just under the picture of Palma Cathedral you can see it in the picture below ringed.Then click on Avatar which is also ringed in the picture below



Step 2) Here you have 2 choices. click on choose file to select a picture you have on your computer or click on show gallery where there is lots of pictures for you to choose from, pick which one you want by clicking on it then you must click on save which again I have ringed in the diagramme below and thats it