How to Upgrade Standalone ESXi 5.0 to 5.1

Download the the offline bundle (depot file) for ESXi 5.1 from here
filename VMware-ESXi-5.1.0-799733-depot.zip

Activate SSH, shut down all your VMs and enter maintenance mode

Upload the file to your datastore

Note: If you run the command with “install” switch, all your personalized drivers of officially unsupported NICs will be deleted. You might consider using the second command with the “update” switch instead (you can add option –dry-run to perform a dry-run only)

esxcli software profile update -d /vmfs/volumes/datastore1/VMware-ESXi-5.1.0-799733-depot.zip -p ESXi-5.1.0-799733-standard

For upgrading to ESXi 5.5:
esxcli software profile update -d /vmfs/volumes/datastore1/VMware-ESXi-5.5.0-1331820-depot.zip -p ESXi-5.5.0-1331820-standard –dry-run

more info

ESXi Free – how to upgrade to ESXi 5.1

VMWare: Update Standalone ESXi 5.0 to 5.1 Using a Depot Zip File

 

you may got error like this:
[DependencyError]
VIB Broadcom_bootbank_scsi-bnx2i_2.70.1k.v50.2-1OEM.500.0.0.472560 requires com .broadcom.cnic_register-9.2.0.0, but the requirement cannot be satisfied within the ImageProfile.
VIB Broadcom_bootbank_net-cnic_1.11.18.v50.1-1OEM.500.0.0.472560 requires com.b roadcom.cnic_register-9.2.0.0, but the requirement cannot be satisfied within th e ImageProfile.
VIB Broadcom_bootbank_net-bnx2x_1.70.34.v50.1-1OEM.500.0.0.472560 requires com. broadcom.cnic_register-9.2.0.0, but the requirement cannot be satisfied within t he ImageProfile.
VIB Broadcom_bootbank_net-bnx2_2.1.12b.v50.3-1OEM.500.0.0.472560 requires com.b roadcom.cnic_register-9.2.0.0, but the requirement cannot be satisfied within th e ImageProfile.
Please refer to the log file for more details.

one option is to run upgrade with -install option instead -update option.
or you may run:
esxcli software vib remove –vibname=scsi-bnx2i
esxcli software vib remove –vibname=net-cnic
esxcli software vib remove –vibname=net-bnx2x
esxcli software vib remove –vibname=net-bnx2

type reboot…

start upgrade process again…

reboot

exit maintenance mode
more info on:
https://communities.vmware.com/thread/482214?start=15&tstart=0