There is three method available, you can use any of them to convert single instance to RAC instance.
a. using dbca
b. using EM
c. using rconfig utility
Here we are converting using DBCA (DataBase Configuration Assistant).
Conversion of single instance database to RAC database using DBCA consists of two part.
In first part, we take the backup of single instance database.
In second part, we convert single instance database to RAC database.
Backup the original single instance database in easy nine steps.
( To see image in large, click on the image)
Templates for existing single instance database has been created.
Go to $ORACLE_HOME/cgftoologs/dbca/templates and check generated backup of single instance.
Steps for conversion of this single instance templates to RAC instance,pl click this link
I'm 10gR2 RAC Oracle certified professional, working from last 6 year in the field of database.