Installing Office 2013 shouldn't lose you any Word or Excel documents, however there is a possibility that your Outlook data file may get overwritten if it's stored in the default location.

Check out Moving Your Outlook Data File and follow the instructions to move your data file into your 'My Documents' folder, once you have done this, you can install Outlook 2013 and point it to the new location for your data file.

Note - This doesn't carry over your email account settings - make sure you know what they are and set them up again in Outlook 2013.

HTH

Neil