Remove a Node From a SQL Server 2008 Cluster

1. Run SQL 2008 setup.exe from the node you wish to remove from a cluster (the node to be removed should be the active node), the Installation Wizard will launch the SQL Server Installation Center as shown below

2. To remove a node from an existing failover cluster instance, click Maintenance in the left-hand pane, and then select Remove node from a SQL Server failover cluster.

3. When you click remove node it will ask you to run the file

4. The System Configuration Checker will run a discovery operation on your computer. To continue, click OK, which will create Setup log files for the installation.

5.  The Installation Wizard will install SQL Server prerequisites if they are not already on the computer which include SQL Server Support Files in this case the prerequisites are already installed, Click Next to continue
   
6. On the Cluster Node Configuration page specify the name of the SQL Server 2008 failover cluster instance that will be modified during this Setup operation, the node that will be removed will be listed in the Name of this node field which auto populated. Click next to continue.

7. The Ready to Remove page displays list of options that will be removed during Setup. To continue, click Remove.

8. During the remove operation, the Remove Node Progress page provides status as shown below

9. On completion remove node page will show the status Complete (success) as shown below, Click Next to continue to go to Complete page which will provide complete summary for the remove node operation
10. The Complete page provides a link to the summary log file for the remove node operation as shown below, to complete the remove node operation click close

11. Continue this operation from other node which needs to be removed.

Ref:

SQL Server 2008 Books Online