On the app:

1. Go to profile
2. Click on your profile photo
3. The app opens our profile photos
4. Click the [+] to add more photos
5. To change the order or to remove, click on any photo
6. Then a window opens called 'Drag & Drop'
7. Press on the photo you want to move, move it to the position you want and release it.
8. To delete a photo, simply click [x]

On the website:
1. Go to 'Edit Profile'
2. Select [upload] or [import]
3. Select a photo and it will be uploaded
4. Now hover over the picture with your cursor. The following options will appear in the picture: [edit] [main] [x] 

[edit] - Select edit to adjust the picture
[main] - Select main to select your profile picture
[x] - select x to remove the profile picture entirely

Note: the x isn't visible on images with a light/white background.