Once you've located the installation file, left-click on it to open the Installation screen. Follow the instructions on the screen. Be sure to read each instruction thoroughly before moving on the next one. When the installation is complete, a shortcut icon to the program is usually placed on your desktop. If not, locate the folder to which you installed the program, and click the .exe file to open it.
Open programs can conflict with the installation process.
Generally, you should shut down the open programs on your taskbar and the programs on the systray area of your taskbar that you know can be shut down, as well as any other programs that you know are running at the time. My daughter has used AIM for some time, we have suddenly started to get the AIM setup screen when Windows loads. I've tried without success to find the offending setup file. It may be a command line in your Autoexec.bat, win.ini, or win.sys files. Unless your are comfortable editing these files, we suggest you don't.