Old sub domain to new main domain

I have subdomain which is doing well on search but I want it to be new root domain which I have already buy how can i do without loosing search authority? (on webmasters tools it says adress changing is restricted to the root domains)

thanks in advance

If you redirect using 301 the Sub-Domain to Root-Domain then the Root-Domain will loose its value. So, internally you can CName with the help of your DNS settings, so that the Root Domain would not loose value.

thanks for the answer can you explain little more i’m tottally new in CName subject (the root domain which i want to use is new so it has no value i think)