Download the file that fits your Operating System:
On Windows, simply install Adobe Reader. The browser will detect the browser plugin if Adobe Reader is installed, and the Adobe Reader installer will install the plugin automatically if you install Adobe Reader.
If you are upgrading from Adobe Reader 6.0.x to Adobe Reader 7.0, uninstall any updates first, in order of installation, then uninstall Adobe Reader. This will ensure a clean upgrade to 7.0.