First access your profile settings by clicking on your icon in top right menu and choose profile tab.
Next click on change profile photo. Then click on select your file to upload a photo or optionally click on take a photo which will use your devices camera to add an image.
To change cover image follow the same steps as above but instead click on change cover image.
you can use any sized image but we recommend a minimum size of 800 x 100 to avoid blurred or stretched images. Larger images you will have the option to crop.