This article explains how to change the MAC address of a physical network adapter on an VmWare ESXi 5.1 host.
1) Connect you with SSH to your ESXi Server
2) Open the file /etc/vmware/esx.conf
3) Search for your old MAC address and replace it with the new one. You can search in the VI editor by typing “/” without brackets.
4) Save your changes by typing :wq