In order for Flash Player to be installed or updated, any programs that use Flash Player must be closed. This includes Internet Explorer or other browsers, instant messengers, Skype, etc.
These programs may be running in the background, not as visible windows, but need to be closed anyway.
To close such programs use the Windows Task Manager. To start Task Manager, take any of the following actions:
•Press CTRL+ALT+DELETE, and then click Task Manager.
•Press CTRL+SHIFT+ESC.
•Right-click an empty area of the taskbar, and then click Task Manager.
Once the Task Manager is running, select the Processes tab. On older Windows version you may need to click on the Process Name or Image Name header to sort the process names.
Now right-click on every process that the Flash Player installer needs to close (e.g. iexplore.exe), then select End Process.