Depending on how your organization has set up Lync 2013, you may be able to save and retrieve your old instant messages. Watch this short video to help you learn if you have that option and, if so, how to change the setting.
Then, if you want more details, see the Help article Save and find your Lync instant messages.
Other videos in this course
This video is part of a training course called Set up Lync 2013.