If your uploaded picture is not showing up click on Actions then Purge cache
If you uploaded the file on the wrong row, just move the file to the right spot and write a new filename for the other one
If you uploaded a duplicate, just edit the filename as example lu10.PNG to lu10-A.PNG
You can replace a wrongly uploaded file with the following steps
Click on the file
Under File history there is a link called "Upload a new version of this file"
Choose a new file and upload it, no need to change the filename!
New version of a file doesn't update right away, it takes time sometimes. Try another browser, the incognito mode, or delete your cache and website settings.