Upgrade ubuntu vm

Ive installed erpnext on my vm and then tried to run upgrade to ubuntu v.16.04 but when try to login gives me error:

We will be back soon.

Don’t panic. It’s not you, it’s us.
Most likely, our engineers are updating the code, and it should take a minute for the new code to load into memory.

Try refreshing after a minute or two.

this is not enough information. share the error logs when you do bench update