You can easily reset the root password on linux-based VMWare appliances through the boot loader. For this to work, you need access to the console of the appliance (i.e. through vSphere (Web) Client), and needs to be performed during offline hours as the appliance has to be rebooted.
Reboot the appliance, and as soon as you see the GRUB boot loader, halt the automatic boot timer by hitting any key (I usually move the selection using the arrows).
Select the first entry, and press e, allowing you to type in some text. At the end of the line that starts with kernel, add the following text:
Do not remove any other text. Then press Enter to confirm.
Press b to continue the boot process. The appliance will boot in single user mode and will not prompt you for a password. As soon as you see the prompt, enter the following command to change the password for the "root" user:
Enter a valid password that's complex and long enough, and remember it.
When the password was accepted, reboot the server:
Do not exit the shell by typing exit as this causes a kernel panic (attempting to kill init).
After the reboot, you should now be able to log on using "root" and your new password.