PowerEdge T110 II Format and Factory Reset

Hi,

sorry if I may have a crude question but I'm not familiar with the Dell Software:

I want to reset a PowerEdge T110 II (for selling it) such that 

• all data are securely erased
• Software is erased too or reseted to factory defaults

I don't know how to manage that. Searching through all the support sites and didn't get a good answer. Is there a possibility to accomplish this via Boot-Manager or with an external boot-CD? Which one should I take then?

Thanks a lot for your help!