How to delete a file attachment from the apachesolr index
From Dileno blog:

If you simply want to delete documents from your Solr index by using the web interface, here's a code snippet that lets you do so:

http://localhost:8983/solr/update?stream.body=
&lt;delete&gt;&lt;query&gt;id:298253&lt;/query&gt;&lt;/delete&gt;&amp;commit=true


This lets you delete documents where the id field matches 298253.

If you want to delete items that matches more than one field, just add another query:

http://localhost:8983/solr/update?stream.body=
&lt;delete&gt;&lt;query&gt;id:298253&lt;/query&gt;
&lt;query&gt;entitytype:BlogEntry&lt;/query&gt;&lt;/delete&gt;&amp;commit=true