Just trying to delete all the documents, and did this:
http://localhost:8983/solr/update?stream.body=%3Cdelete%3E%3Cquery%3E*:*%3C/query%3E%3C/delete%3E <
http://localhost:8983/solr/update?stream.body=%3Cdelete%3E%3Cquery%3E*:*%3C/query%3E%3C/delete%3E
Probably you are missing a forward slash (/) after update and before question mark.
/
Current query:
http://localhost:8983/solr/update?stream.body=*:*&commit=true
Revised query:
http://localhost:8983/solr/update/?stream.body=*:*&commit=true