Step 1:- Examine the Oratab file (/var/opt/oracle/oratab in Solaris) to identify the instance dependencies on this oracle home. 

Step 2:- Start DBCA, selects Oracle Real Application Clusters Database, select Delete a database, and selects the database that you want to delete. Repeat this step to delete all databases. 

Steps 3 connect with ASM instance, run the following command:

a) Check disk group which are using by ASM instance:

select * from V$ASM_DISKGROUP;

b) Drop the disk group.

drop diskgroup including contents; 

c) Shut down ASM on all RAC nodes, and verify that all ASM instances are stopped.

e) To remove the ASM entry from the OCR, run the following command for all nodes on which this Oracle home exists:

srvctl remove asm -n nodename 

Step 4 Remove oracle home (On All Node)

Go to $ORACLE_HOME/oui/bin and execute ./runInstaller. Start OUI, and remove any existing Oracle Database 10g with RAC software by selecting Deinstall Products and selecting the Oracle home that you want to remove. 

Step 5 Remove oratab entries for the deleted Oracle home databases. 

Step 6 De-Installing Oracle Clusterware

a) Go to $CRS_HOME/install directory and execute rootdelete.sh script (On All node)

# /export/home/oracle/product/10.2.0/crs/install/rootdelete.sh

This will disable the Oracle Clusterware applications that are running on the cluster node.

b) Run the script CRS_home/install/rootdeinstall.sh on a local node to remove the OCR.

c) Go to $CRS_HOME/oui/bin and execute. /runInstaller.  Start OUI. In the Welcome page, click Deinstall Products to display the list of installed products. Select the Oracle Clusterware home to de-install (Execute on All Node)