How can I activate the version 5.7.1 so that is enabled development tool?
If you have Develop deactivated you seem to have the CC version installed. If you have a CC subscription, sign out and back in: https://helpx.adobe.com/creative-cloud/help/sign-in-out-activate-apps.html
If you have a standalone license code for LR 5 you need to remove the CC version installed and install the standalone version from here: Windows, Mac
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