Once you've picked one of the logos out, go inside and change the costume to bitmap otherwise it won't work. Then right click on the costume and click on the thing that says "save to local file". Then hit save (when the documents tab pops up). Go to your profile and then put your mouse on top of your profile pic. Next, a thing that says "Change" should appear. Click on that and the documents tab should pop up. double click the picture with your selected logo on it. Near the middle top part of your screen, there should be something that says "Thumbnail changed". Then go to something else like another project and then look at the thing next to your stuff and your profile should've changed. If it did not, tell me in the comments!