This page discusses how to remove SharePoint from servers in the farm:

1. Log in to each of the SharePoint servers in the farm

2. Run the SharePoint Configuration Wizard on each of the Web Front End servers and unjoin them from the farm. Provided no Web Apps were built outside of SharePoint's control, they should be automatically deprovisioned along with the web sites.

3. Run the SharePoint Configuration Wizard on the App server, and choose to remove it as the last server in the farm.

4. Go into SQL Management Studio and remove the Configuration, Content, and Service Application Databases. Be sure to not delete other databases. Made them first read only for a few days, and if there are no errors, delete them. 

5. Rejoin servers and recreate the farm to your new specifications.

Also check out the overview of SharePoint 2010 Best Practices at: