http://www.avast.com/uninstall-utility
Several recent posts by knowledgable people say the instructions are incorrect. Why haven’t they been fixed at the official download link above?
Supposedly proper procedure is to run this utility in normal mode (not safe mode). It then asks permission to restart computer in safe mode to complete the uninstall.
I haven’t tried it (yet), so don’t know what is correct.
I won’t advocate for Safe Mode in normal conditions.
But I would if “anything” goes wrong. In Safe Mode, the uninstallation works all the time.
Yes you don’t need to boot to safe mode first, just run the Avastclear tool and it will then ask for permission to boot to safe mode where it will continue to do it job.
Note that the tool is meant to be used after first uninstalling Avast normally then running the Avastclear tool will remove remnants or in the event Avast cant be removed normally then proceed with running the Avastclear tool directly.
These instructions work:
Successfully Installing Avast 
You’re the only one who seems to understand the purpose of my post. If avast doesn’t care to make the instructions precise, that’s their problem (not mine). Fortunately I had read about this error beforehand otherwise might have become discombobulated! ???
FWIW, I ran the avastclear tool in normal mode on a W7 computer and it offered/recommended the option to proceed in safe mode. I did so and it worked OK. The only remnant of avast I’ve noticed thereafter is in the customize systray icons list, where it remains, but that could be a Windows fault. I’ve noticed that uninstalled software may still have an icon in that list, even so-called portable versions. No big deal, if you don’t worry about such little things.
After removing avast from the W7 computer, I activated Windows Defender. Then Windows Update offered MSE as an option, which I accepted. That’s a lot easier to maintain than avast, pretty much automatic after it’s set up. I also use it on a W8.1 computer.
I’ve been an avast user for a long time, but only have it now on my XP SP3 computer. I doubt that I’ll do any more of the program updates there. It’s working OK, and I don’t have the time or inclination to keep up with all of the wonderful new changes in avast. I just need something simple and stupid. :
Cheerio! 
I just need something simple and stupid.There are many of those to be found. Security Essentials is just one. Even Microsoft admits that Security Essentials isn't the best. You do the search. It's also your computer. :)
The reason for rebooting into safe mode is while in normal mode some low level drivers remain.
To more completely remove the low level drivers you need to reboot into safe mode.
Read this about Microsoft and third party anti-virus software…
http://www.howtogeek.com/173291/goodbye-microsoft-security-essentials-microsoft-now-recommends-you-use-a-third-party-antivirus/
Avastclear.exe must be used in regular mode in order to give permission to UAC for the program to run. I wasted and hour with it not working in safe mode. Thanks Avast.
Trying to use avastclear.exe just about tops off a horrible experience on a friend’s laptop. He tried to renew and install Avast Internet Security 2015. It disabled his onboard keyboard and did not allow the computer to recognize USB keyboards. “Free” Avast support took advantage of the situation and charged him a huge amount to damage files on his other computer and never helped with the laptop. They also charged him for Grime Remover. A $29 expense turned into $250 experience. Enabling the onscreen keyboard through ease of access allowed me to work on the computer. Uninstallation of Avast re-enabled the onboard keyboard.
I had recommended and installed Avast for many friends and clients, with the caveat to never call “free” support. It’s time to find a new anti-virus program to folks, if Avast can’t keep their house clean.
Report your experience to Vojta Nekvapil: nekvapil[at]avast.com (3rd Party Support Manager)