As far as I'm aware update manager is intended to integrate with vCenter. You can install it on a separate Windows server but it requires vCenter to operate.
Bedde
Do you have access to download the ESXi souce from VMWare as a licensed product?
If you upgrade 4.1 to 5x and you don't have a valid 5x license it will run in eval mode for 60days, after which you will have to revert to the free version.. (which may be OK depending on your requirements)
It would be helpful if you could answer the previous questions.