Hi Frank,
You're registered on SCN via your OSS account (a.k.a. S User account) that was issued to you through your employer. Certain information is pulled from this account into SCN and therefore cannot be changed from this platform.
You'll have to contact the administrators at your company, from whom you received your account information from, and ask them to update your details.
Also check out: https://websmp101.sap-ag.de/FAQs > HOW DO I UPDATE MY CONTACT INFORMATION?
About multiple accounts, most SCN members move on to a new account after they end their relationship with the company where their S-User Id was issued. While SCN cannot migrate points and history at the moment, the functionality should be restored soon.
Jason