I saw that it must delete Alwill software/Avast4/setup/awast.setup (9kb) and then copy new and correct file.
You are confusing two actions/problems.
1. The avast.setup is used for the updates and must be allowed Internet Access by your firewall.
2. The servers.def contains a list of the servers to use when updating, if this becomes corrupt, usually 0KB in size then you need to replace it.
The first thing to do is ensure your firewall allows access to avast.setup, this is more likely to be the problem if your C:\Program Files\Alwil Software\Avast4\Setup\servers.def file is 9KB (8,744 bytes), which is the correct size.