update README.md

Author: funbringer

README.md

@@ -77,6 +77,19 @@ Done! Now it's time to setup your partitioning schemes.
 
 > **Important:** Don't forget to set the `PG_CONFIG` variable in case you want to test `pg_pathman` on a custom build of PostgreSQL. Read more [here](https://wiki.postgresql.org/wiki/Building_and_Installing_PostgreSQL_Extension_Modules).
 
+## How to update
+In order to update pg_pathman:
+
+1. Install the latest _stable_ release of pg_pathman.
+2. Restart your PostgreSQL cluster.
+3. Execute the following queries:
+
+```plpgsql
+/* replace X.Y with the version number, e.g. 1.3 */
+ALTER EXTENSION pg_pathman UPDATE TO "X.Y";
+SET pg_pathman.enable = t;
+```
+
 ## Available functions
 
 ### Partition creation
@@ -654,3 +667,4 @@ Do not hesitate to post your issues, questions and new ideas at the [issues](htt
 Ildar Musin <i.musin@postgrespro.ru> Postgres Professional Ltd., Russia		
 Alexander Korotkov <a.korotkov@postgrespro.ru> Postgres Professional Ltd., Russia		
 Dmitry Ivanov <d.ivanov@postgrespro.ru> Postgres Professional Ltd., Russia		
+