Download Autotune from the Antares website. Antares offers time-limited demos for all versions of Autotune, which have no other limitations on them.
Double-click the downloaded file to run the installer. If you're using a custom VST plugins directory, specify this directory in the installer window. Click "Next," then "Finish" to complete the installation.
Double-click the FL Studio desktop icon to launch it. Click the "Insert 1" channel. Click the arrow next to the first insert effect slot on the right-hand side of the window. Click "Select," then "More."
Click Refresh, then "Fast Scan." Click the entry for Autotune to load it. Click "Autotune" in the effects section to open the Autotune VST plugin window.