You can Download a Windows 10 RS1 .iso and perform a clean installation: [URL] 
I buy optiplex 380 from 2nd hand pc seller. This pc have Windows 7 Pro COA, but the installed OS is Windows 7 Ultimate. The recovery partition was missing and i dont have any recovery disk. Where i can download windows 7 pro to reinstall this pc?. Sorry for my bad english
Can i reinstall windows 7 professional on optiplex 380?