Adobe is discontinuing development of Flash for Linux. It is a good idea
not to try to upgrade unless things aren't working well. You will not have
to wait till 12.04 because you cannot expect any change since Flash is
proprietary software.

Chrome does not require you to install Flash. It comes with it built in.
Firefox will need you to install Flash. You do not say what file format it
is. If it is a .deb file then you can click on it and it will open in
either Software Centre or Gdebi depending on your version of Ubuntu.
However, if it is a binary file then you will have to make it
executable first. To do that you right click and go to Properties and check
the box on the r Permissions tab to make it executable.

If all fails then completely remove Flash using Synaptic. Then clean the
cache and re-install. If you do not clear the cache then it will just
re-install what you have already downloaded rather than get a fresh copy.

The command for cleaning the cache is sudo apt-get clean. If you are on
dial-up this is probably not a good idea since it will remove the
downloaded copied of all installed debs. If you are short on HD space on
your home folder this is a good command to remember to free up disk space.
If you only want to remove one package then use sudo nautilus (or sudo
dolphin for KDE) from a terminal. Then navigate to /var/cache/apt/archives/
in the root directory and remove the one package.

If this is way too much for you then try Chromium which is in
the repositories or Chrome from Google.