Giulia, Try this…
Open AVG.
In the top menu click Options, and then click Advanced Settings.
In the left part of the Advanced Settings window double-click Update to show further options.
Click Manage, and then click Delete temporary update files.
Tip: If double-clicking Update does not show the Manage option, click the [+] icon next to Update.
Restart your computer.
Open AVG again, and then click Update now to make sure your AVG is up to date.
AVG Guru
Last week I have renewed my antivirus licence.
The installation went ok, but now there are problems and it seems it cannot download any updates. It starts downloading them and then it stops around 30%. I've tried waiting, restarting and whatever, but with no success.
The old version worked just fine.
Giulia, Try this…
Open AVG.
In the top menu click Options, and then click Advanced Settings.
In the left part of the Advanced Settings window double-click Update to show further options.
Click Manage, and then click Delete temporary update files.
Tip: If double-clicking Update does not show the Manage option, click the [+] icon next to Update.
Restart your computer.
Open AVG again, and then click Update now to make sure your AVG is up to date.
AVG Guru
OK Giulia, No probs…
AVG Guru
Thank you very much!
I've just tried and now everything seems to work just fine 
Thank you very much!
I've just tried and now everything seems to work just fine