Update faq.md (infiniflow#685)

### What problem does this PR solve?

Updated FAQ: How to upgrade RAGFlow

### Type of change

- [x] Documentation Update

docs/faq.md

@@ -382,7 +382,14 @@ This error occurs because there are too many chunks matching your search criteri
 
 ![topn](https://github.com/infiniflow/ragflow/assets/93570324/7ec72ab3-0dd2-4cff-af44-e2663b67b2fc)
 
-### 9 How to update RAGFlow to the latest version?
+### 9 How to upgrade RAGFlow?
+
+   You can upgrade RAGFlow to either the dev version or the latest version 
+- Dev versions are for developers and contributors. They are published on a nightly basis and may crash because they are not fully tested. We cannot guarantee their validity and you are at your own risk trying out latest, untested features.
+- The latest version is stable and reliable, and works best with RAGFlow users.
+
+
+   Update RAGFlow to dev version:
 
 1. Pull the latest source code
    ```bash
@@ -403,3 +410,30 @@ This error occurs because there are too many chunks matching your search criteri
    ```bash
    docker compose -f docker-compose-CN.yml up -d
    ```
+
+To upgrade RAGFlow to latest version:
+
+1. Update **ragflow/docker/.env** as follows:
+   ```bash
+   RAGFLOW_VERSION=latest
+   ```
+2. Pull the latest source code:
+   ```bash
+   cd ragflow
+   git pull
+   ```   
+
+3. If you used `docker compose up -d` to start up RAGFlow server:
+   ```bash
+   docker pull infiniflow/ragflow:latest
+   ```
+   ```bash
+   docker compose up ragflow -d
+   ```
+4. If you used `docker compose -f docker-compose-CN.yml up -d` to start up RAGFlow server:
+   ```bash
+   docker pull swr.cn-north-4.myhuaweicloud.com/infiniflow/ragflow:latest
+   ```
+   ```bash
+   docker compose -f docker-compose-CN.yml up -d
+   ```