How to clear a Solr 4 index
It’s actually quite easy to do - all you need is a browser, doesn’t matter which one.
First go to this page..
http://localhost:8983/solr/update?stream.body=<delete><query>*:*</query></delete>
Then go to this page..
http://localhost:8983/solr/update?stream.body=<commit/>
localhost:8983 might be different on your system depending on how you have set you your instance of Solr.
You can find this and other information in the Solr FAQ