Using the upgrade page I'm seeing:

Error: 521: HTTP/1.1 521 Origin Down

It looks like it's an error from Cloudflare

Are you using Cloudflare ?
I'm not sure it comes from you because i've got the same error when I go to http://codoforum.com/blog
So maybe the upgrade redirect to something offline too

Here's a link from Cloudflare support: https://support.cloudflare.com/hc/en-us/articles/200171916-Error-521

Hi,

Can you try upgrading again ?

There was a mistake in my reply, i've got the error 521 when i go to https://codoforum.com/blog and not http://codoforum.com/blog
The link "Blog" on the forum's header points to https, i think that's what caused the error

Hi,

Same here:

1.0> Checking for latest version
1.1> Connecting to server: codoforum.com ...
####: Initiating cURL request
  Error: 521: HTTP/1.1 521 Origin Down

Same 521 code on codoforom.com websites.