Modify section title for manual downgrade/upgrade (#392)

Updated the section title to include 'upgrade' alongside 'downgrade' for
clarity.

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Documentation**
* Updated documentation structure and headings to better reflect
coverage of both downgrade and upgrade procedures for Unraid
* Reorganized downgrade section with two distinct methods presented via
separate tabs: simplified graphical interface method and command line
method
* Each method includes detailed step-by-step instructions specific to
that approach

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: 1JorgeB

docs/unraid-os/system-administration/maintain-and-update/upgrading-unraid.mdx

@@ -139,7 +139,7 @@ If you have access to the WebGUI, you can go to **Tools → Downgrade OS.** This
 
 If you don't see the option to downgrade under **Tools → Downgrade OS**, use the manual method described below. This usually means that the files for the previous version are not on your flash drive.
 
-### Manual downgrade
+### Manual downgrade or upgrade
 
 Manual downgrades are only needed if you can't access the %%WebGUI|web-gui%% or if the downgrade option isn't available. Before proceeding, it's important to back up your USB flash device. For more details, see [Backing up your flash device](../maintain-and-update/changing-the-flash-device.mdx#backing-up-your-flash-device).