I am new to DNN, but not to CMS systems and I understand why there may be better ways to do this.
None the less, there comes a time in the life of most CMS systems and admins, that access to the dB is the only thing that cuts it. When you reach this point you need to know how to add the DNN dB to your MS SQL Management console (attach a dB for editing). Depending on what version and how you built your site you may or may not ever be able to do this.
I found that if I used the default installs I was never able to attach DNN's dB to the MS SQL Express Console and still have IIS/ASP DNN dB access work. I then when back and installed DNN using a 'real' dB user account (SQL access not that evil MS account access stuff). To do this I had to edit the connection string in the web.config file for MS SQLExpress and install my site. Once I got the access string right (a normal hell of writng XML instead of much simpler name:value pairs like most other's do it - and the same hell Java puts you through all the time) things were fine, and I could see the DNN dB in the console and edit table values as needed using regular SQL queries.
There may be a way of adding the DNN dB to your console that does not break IIS/ASP after install, but I never found it. so get this all right up front or risk loosing lots of work.
If someone else gives you a step by step, great. If not, be prepared to re-install and get console access right, then do whatever you need. The good news is, once the console sees the dB you can do all the regular dB backups and other management just like you would with any other dB based app. Until then, I have no idea how you could get to stuff outside of the GUI or writing code to call the dB directly via DotNet tools.