When you purchase the latest version of CircuitStudio you may use the new license on an older version of the software. The license activation downloads the appropriate *.ALF file for the version of CircuitStudio being activated.
Old versions may be downloaded here (requires your CircuitStudio login):
Evaluation Version (same software, different installer doesn't require sign in to run installer):
https://altium-release-manager.s3.amazonaws.com/CircuitStudio_1/CircuitStudioSetup_1_5_2_eval.exe is version 1.5.2 Evaluation Installer.
Offline version - special request only:
A special offline installer is available by request, that is designed for offline sites and once installed, the checking for future updates is not functional (and can appear to work so is misleading if this functionality is not fully understood). If you require this special installer, please contact support on software (at) element14 dot com.