[ci skip] Fix incorrect routing description
Close #4079
diff --git a/user_guide_src/source/installation/upgrade_300.rst b/user_guide_src/source/installation/upgrade_300.rst
index 971f9e4..4b3b408 100644
--- a/user_guide_src/source/installation/upgrade_300.rst
+++ b/user_guide_src/source/installation/upgrade_300.rst
@@ -266,8 +266,7 @@
However, what happens if you have an *application/controllers/admin/*
directory and the user visits ``http://example.com/admin/``?
In CodeIgniter 3, the router will look for a 'Main' controller under the
-admin/ directory as well. If not found, it will fallback to the parent
-(*application/controllers/*) directory, like in version 2.x.
+admin/ directory as well. If not found, a Not Found (404) will be triggered.
The same rule applies to the '404_override' setting.