Hi,

Uninstalling a SQL Server Clustered Instance

http://www.mssqltips.com/sqlservertip/2172/uninstalling-a-sql-server-clustered-instance/

http://www.youtube.com/watch?v=-rUCyxlossk

http://blogs.msdn.com/b/sqlserverfaq/archive/2010/04/23/how-to-un-cluster-sql-server-2005-cluster.aspx

sql 2008 r2 sp1 upgrade active/passive node

http://social.msdn.microsoft.com/Forums/sqlserver/en-US/bd3e5382-1cbd-4b6f-83a3-19470850e1a4/sql-2008-r2-sp1-upgrade-activepassive-node?forum=sqlsetupandupgrade

Uninstalling a SQL Server Clustered Instance

http://www.mssqltips.com/sqlservertip/2172/uninstalling-a-sql-server-clustered-instance/

Dealing with SQL in the SFW-HA cluster will add a couple extra steps.
You can do the following because your primary node works:

1. In VCS remove the passive node from the available node list for the SQL service group.
   (In VCS...Click the service group on the left -> Click Tools at the top -> "System Manager...")
2. Uninstall and reinstall SQL, you can install locally on the passive node.
   (Keep the same Instance name)
3. Run the SFW-HA SQL wizard to add the passive node back to the service group
   
   Notes on step 3:

1. Run the SFW-HA SQL configuration wizard from the active primary node only (This is critical)
2. The  SFW-HA SQL wizard uses the paths from the node where the wizard is run
3. This will change the local paths, on the passive node, to point back to the shared storage
4. This will also get the passive node’s instance back under the context of the virtual server name

If you run into any problems please feel free to open a support case with us. We are here to help.