Document updating changes, rather than replacing them

These docs are from 2009, when maybe this was a common way of referring
to updates of changes, in the present day and age the term isn't really
used and is just a bit confusing.

NOTE: Anchor was not updated to avoid breaking existing references.

Release-Notes: skip
Change-Id: Ib0072b7abcb98fc3a22e55cd38054535ee25f161

Documentation/user-upload.txt

diff --git a/Documentation/user-upload.txt b/Documentation/user-upload.txt
index 415d27c..16ab0d7 100644
--- a/Documentation/user-upload.txt
+++ b/Documentation/user-upload.txt
@@ -518,7 +518,7 @@
 
 
 [[push_replace]]
-=== Replace Changes
+=== Update Changes
 
 To add an additional patch set to a change, ensure Change-Id
 lines were created in the original commit messages, and just use
@@ -719,9 +719,9 @@
 For more details on using `repo upload`, see `repo help upload`.
 
 [[repo_replace]]
-=== Replace Changes
+=== Update Changes
 
-To replace changes, ensure Change-Id lines were created in the
+To update changes, ensure Change-Id lines were created in the
 commit messages, and just use `repo upload`.
 Gerrit Code Review will automatically match the commits back to
 their original changes by taking advantage of their Change-Id lines.