i lost my licence number who will help
You don’t say what version you have, so I have to assume that it is one of the paid versions of avast.
Try the Resend avast License http://www.avast.com/resend-license-paid.php, you will need to enter the email that you used when purchasing the license, e.g. the one that the original email with the link was sent.
Note: this is the beta sub-forum, this should have been in the main avast! Free/Pro/Suite forum.
For the free license:
http://www.avast.com/resend-license-free-antivirus.php