I need to know how to activate the navigation system and connect my cellphone.

There is no "download" for a 2008 vehicle. It requires a DVD disc. If you do not have it, you'll need to obtain one. You can try various sources online via a web search. There are a significant amount of Internet resources on these - simply do a search to find the disc or discs you need. As far as instructions, download a copy of the owners manual to learn more. https://www.mbusa.com/vcm/MB/DigitalAssets/pdfmb/ownersmanual/2008_sl550_sl55amg_sl600_sl65amg.pdf