You'll either need to obtain the password from the registered owner/seller, or do a ground up clean install of Windows onto the system (use the MS Media Creation tool to build a flash drive to do the install).  
After pressing F8 key I have no possibility to Dell Datasafe restore after pressing F8. (last possibility is DOS prompt). I bought the laptop from someone but apparently it is secured by an administrator and I don't have the password. Only mine as a user.
Second owner, do not have Admin password