[Plugin: Fast Secure Contact Form] Upgrade doesn't work

Hello.
I have a problem when upgrading plugin from 3.0.5 to 3.1.3.1. (Upgrade to previous version <3.1.3.1 have behaved the same).
A page with the following text just stands…:
“
Refreshing update

The update process is starting. This process may take a while on some hosts, so please be patient.

Updating Plugin Fast Secure Contact Form (1/1)
“

When after a 5 or more minutes trying to go to some other link in admin panel the following shows:
“
Briefly unavailable for scheduled maintenance. Check back in a minute.
“
Also, when calling a site.

PLease any advice. Thanks.