Update upgrade documentation (#526)

Author: dhurley

hugo/content/upgrading.md

@@ -10,24 +10,55 @@ categories: ["configuration"]
 doctypes: ["task"]
 ---
 
-## Upgrade the NGINX Agent
+## Upgrade NGINX Agent from version v2.31.0 or greater
 
-To upgrade the NGINX Agent, take the following steps:
+{{< note >}} Starting from version v2.31.0, NGINX Agent will automatically restart itself during an upgrade. {{< /note >}}
 
-1. Open an SSH connection to the server where you’ve installed the NGINX Agent and log in.
+To upgrade NGINX Agent, follow these steps:
+
+1. Open an SSH connection to the server where you’ve installed NGINX Agent and log in.
 
 1. Make a backup copy of the following locations to ensure that you can successfully recover if the upgrade has issues:
 
     - `/etc/nginx-agent`
     - `config_dirs` values for any configuration specified in `/etc/nginx-agent/nginx-agent.conf`
 
-1. Stop the NGINX Agent:
+1. Install the updated version of NGINX Agent:
+
+    - CentOS, RHEL, RPM-Based
+
+        ```shell
+        sudo yum -y makecache
+        sudo yum update -y nginx-agent
+        ```
+
+    - Debian, Ubuntu, Deb-Based
+
+        ```shell
+        sudo apt-get update
+        sudo apt-get install -y --only-upgrade nginx-agent -o Dpkg::Options::="--force-confold"
+        ```
+
+
+
+## Upgrade NGINX Agent from a version less than v2.31.0
+
+To upgrade NGINX Agent, take the following steps:
+
+1. Open an SSH connection to the server where you’ve installed NGINX Agent and log in.
+
+1. Make a backup copy of the following locations to ensure that you can successfully recover if the upgrade has issues:
+
+    - `/etc/nginx-agent`
+    - `config_dirs` values for any configuration specified in `/etc/nginx-agent/nginx-agent.conf`
+
+1. Stop NGINX Agent:
 
     ```shell
     sudo systemctl stop nginx-agent
     ```
 
-1. Install the updated version of the NGINX Agent:
+1. Install the updated version of NGINX Agent:
 
     - CentOS, RHEL, RPM-Based
 
@@ -43,8 +74,8 @@ To upgrade the NGINX Agent, take the following steps:
         sudo apt-get install -y --only-upgrade nginx-agent -o Dpkg::Options::="--force-confold"
         ```
 
-1. Start the NGINX Agent:
+1. Start NGINX Agent:
 
     ```shell
     sudo systemctl start nginx-agent
-    ```
+    ```