Hi…always been a happy user of Avast … Currently use Avast Free 4.8…which is the best way to install the newest version…how come “program update” doesn’t give you the option to download 5.1? Do I need to use a program uninstaller tool? Thanks
run Uninstall Utility & uninstall previous version
http://files.avast.com/files/eng/aswclear5.exe
Download Your Appropriate Version Here
Free AV: http://files.avast.com/iavs5x/setup_av_free.exe
Pro AV: http://files.avast.com/iavs5x/setup_av_pro.exe
Internet Security: http://files.avast.com/iavs5x/setup_ais.exe
Use Your Existing License
Download latest version and the removal tool and save, then uninstall 4.8 via add remove program’s and reboot, run ccleaner then reboot into safe mode and run the removal tool and reboot again, run ccleaner again and now your clear to install avast 5.1.864.
If you have any issue’s please respond back in this thread 
Once you open the removal tool scroll down to the version that you are removing and click.
+1 
Craigb has made an important clarification. I also recommend running aswClear.exe (Clean up Tool) in SAFE MODE as it has shown that there are remnants left if not run in safe mode.
Here a usufull article from the Knowledgebase :
http://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=504&nav=0%2C2%2C41
But in this case you have to select Avast! 4.8 from the drop-down menu of aswclear5.exe.
Greetz, Red.
I ran it in safe mode as since installing 5.1.864 it has created havoc on my win xlp system by beeping and not having my video enabled at start up. Have to shut down via power button several times to sometimes get a normal start up.
Tried the uninstall tool in safe mode and it made things worse and finally got it to boot up and it left many remnants of avast on computer.
Tried to install MSE but was missing some componants so re-installed avast 4.8 which upgraded to the same 5.1.864 that I just tried to uninstall and the same video problems continue.
Very dissatisfied with Avast as it has just about ruined my computer and uninstall didn’t work.
Anyone have advice?
Thanks,
Ken.
Please start your own thread as ‘littlebit 1’ is the initial OP on this thread. Your issues may be totally different. BTW…I have used aswClear numerous times in safe mode for many versions, beta and otherwise,and have never had a problem. :-\
Ran the uninstaller in safe mode and it left many fragment behind.
Since this latest upgrade to avast 5.1.864, it takes a few tries to get my computer to boot with the video working so after doing this in safe mode it took about 5 tries to successfuly get my computer to start.
Can the uninstaller be run in normal mode or is that not advised?
Anyone else have this same problem if the uninstaller doesn’t work correctly, is it safe to manually delete all avast remnants from computer?
Also, is Avast working on a fix that will correct this serious problem that I now have with my computer since this update?
Ken.
Try the new .874 pre-release at http://forum.avast.com/index.php?topic=68927.0;topicseen . Most users are reporting success with fixing .864 issues.