is it possible to upgrade vsphere esxi 5.1 to 5.5 without re-importing the virtual machine,or even without shutting down the virtual machine, and if so how?
Hi and welcome to the forum,
if you not have the posibility to move your VM to an other host, than you do not have the option to not power them down.
Check out the following website for how to upgrade.
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=205835...
Frank
You can upgrade the ESXi host using the vCLI
vSphere 5.5 Documentation Center
