Frist grab the release from the cisco page here

Then put it through scp from you Download place to the ESX Server

scp CiscoAVS_1.5-5.2.1.SV3.1.5-pkg.zip root@10.32.5.150:/tmp
Password:
CiscoAVS_1.5-5.2.1.SV3.1.5-pkg.zip 100% 35MB 806.2KB/s 00:45

Next you Login to the ESX through SSH and check the current version

~ # vemcmd show version
VEM Version: 5.2.1.3.1.3.0-3.2.1
System Version: VMware ESXi 5.5.0 Releasebuild-2068190
ESX Version Update Level: 0

Then i unzipped the archives and upgraded the vib

cd /tmp/
unzip CiscoAVS_1.5-5.2.1.SV3.1.5-pkg.zip
unzip CiscoAVS_1.5-5.2.1.SV3.1.5.zip
cd ~
esxcli software vib update -v /tmp/CiscoAVS_1.5-5.2.1.SV3.1.5/cross_cisco-vem-v197-5.2.1.3.1.5.0-3.2.1.vib --maintenance-mode

And thats it, i’m now running the new AVS Version

~ # vemcmd show version
VEM Version: 5.2.1.3.1.5.0-3.2.1
OpFlex SDK Version: 1.1(1j)
System Version: VMware ESXi 5.5.0 Releasebuild-2068190
ESX Version Update Level: 2