You always want to uninstall any anti-virus program if you decide to use another...see link below. As for Avast, all you need to do is go to their homepage:

Avast download

Here is a link that might be useful: Uninstall AVG

If you can't find it anywhere, including the Control Panel, you may be ok...or there may be remnants still on your computer. If you want to be sure it's gone, you might want to reinstall AVG, and then uninstall it. Or, if that is too troubling to consider, just install Avast and keep your fingers crossed. Did you do a system restore to try to make AVG go away? Usually it's better to simply uninstall something directly.

Note also that there are two versions of the home-free product, v4.8 and 5 which is relatively new. I have experienced issues with v5 in some installations. A free registration number will be required also.

Do I uninstall avg first and then install avast ? Or can I do the new installation of avast first , giving me protection in the meantime?
salbwil

salbwil-
Having two antivirus programs installed on the computer at the same time can cause problems. It's unlikely anything bad will happen between the time you uninstall AVG and install Avast. If this brief breach in security makes you nervous, you can:
1) Download Avast
2) Close all your browser windows
3) Uninstall AVG
4) Install Avast

And, in any case, run a full scan with Avast immediately.

Be sure to update Avast before running the full scan. I have Avast version 5 and it has worked perfectly for me. The interface is much better than on the older version.

download Avast to your pc do NOT install it, then uninstall AVG use the removal tool specific for AVG, once it is fully gone then go to your Avast download and double click to install it. Once you have done that you will need to follow the directions to get your registration number and insert it into your AVAST.
Antivirus Product Removal Tools

Just wondering...have heard mixed opinions re Avast5 ...should I just wait until it's sorted and continue with 4.8?

And if/when I DO get 5, will it over-write 4.8 or should I uninstall it first?

Regards,
Shax

I am still using 4.8 there is no big rush to go to 5 since 4.8 will be supported for quite some time, I personally like to wait a while and let them iron out all the bugs, let the ones that rush in find out all the problems, before I update.
There have been several significant bugs popping up that they are working on and fixing. Some may have no problem at all where as some might never know since every system is different. I posted about some of them on the AVAST5 thread here.
So that decision is totally up to you.
You can put 5 over 4.8 as part of it's install process it will remove the old version however many people prefer doing a removal first, you will get both answers on this one.

Just had an interesting experience. Using Opera 10 browser I was searching to see if there was such a thing as OE available for download that could be used on Windows 7. Using Google, I clicked on one topic on the right hand side (paid listings?)and immediately Avast popped up with a warning of a malicious site and closed the browser window. I am really thankful for a security program that will react that quickly to a threat.