Step2-> Open profile anyone who has locked profile picture or whom locked profile picture you want to see.
Step3-> Now "Right" click on profile picture and Copy Image Location ( Image URL )
Step4-> Now open "Notepad " then right click in it and "Paste" Image URL
URL Just look like below
Step5->Now remove 160x160 from link and add 720x720
Step6-> Now copy this modified link and paste it in to New Tab address bar and hit enter.
Now You have done . Now You can see locked profile picture in large size . :)