Always uninstall the old version first, makes a mess of your desktop but
avoids other problems. Turn off AV software and security software if you
have it. Reboot before uninstall, reboot after and make the new install
before doing anything else, have the installer package already downloaded
and on your desktop so it's easy to find.
Video drivers will bite you if they get upset during install, especially
with the 64 bit version.
I suggest you always keep a copy of the installer package somewhere so
that next time around if a new version gives you trouble (and that does
happen) you have a nice clean way of going back just by repeating the
above but using the older package.
A lot of people have trouble with video drivers and it seems like trying
to overwrite the old ones can't always be done, then you end up with half
old half new and blue screen. It does work sometimes but then you never
quite know how safe you are
This is why you will be advised not to let
Windows Update do it for you, it's not because the drivers are different,
only the method can fall over...