You don't, live or suspect viruses are not to be uploaded to the forum.
Send the sample to
virus@avast.com zipped and password protected with the password in email body, a link to this topic might help and undetected malware in the subject. If you zip and password protect the sample you may be able to send it in the normal way through gmail (sorry I don't use gmail).
You could also check the offending/suspect file at:
VirusTotal - Multi engine on-line virus scanner and
report the findings here. VirusTotal do send samples to contributing AVs if they don't detect it, but it is always best to send the sample directly to avast.
