Well if you have nexus os and want to update it , it is similar to cisco ios.
1.download the image from cisco.com , this time you need to download two images , the kick start , and the OS image ( note they must match in ver )
2.u need ftp , tftp , scp whatever
3.login to the Nexus 5k , type copy tftp: bootflash: … if you are using management interface make sure when it ask for you which vrf to type management or u will get confused as it will give error not reachable
4. copy both files the start kick and the OS
5.now type install all kickstart bootflash://n5000-uk9-kickstart.bin system:n500-uk.n1.bin
thats all 🙂