This is a user-to-user help forum. We don't work for Polycom/Obihai. The large majority of the regular users here on this forum do not have any experience with the 508 products, so you're not going to get expert instructions on using its specific features.
However, most of its functions are shared with the simpler products, such as the 200 (one physical phone port and four logical service provider slots) or the 202 (two physical phone ports and four logical service provider slots).
Before asking a lot of basic questions that will no doubt annoy experienced users, you may want to read through the administration guide to understand more about the underlying technology and settings. You can also browse through the many answered questions here, to see that others have asked those questions already.
For example, one of your questions asks how to edit a value in Expert mode. This is one of the most frequently asked questions. You need to remove both check marks to the far right of the parameter and its default settings, so that you can override those settings. After manually editing a setting, you need to scroll down and click "submit" and wait a few minutes while the portal remotely applies the setting to your device.
As for firmware updates, there are probably hundreds, if not thousands of posts on this topic; in fact, there is an entire section of this forum on that topic.
Obihai has done a really poor job with firmware management over the years. There have not been any release notes in years, and the current versions have not been posted here in this forum by the company. Volunteers often post links to download the firmware manually.
The portal has the ability to push firmware updates to your device automatically. You also can dial ***6 to check for new versions, but that method often gives a false negative answer (no firmware update available).
Google recently completed a massive redesign of its Google Voice infrastructure. It required firmware updates to the Polycom products to keep working. Firmware updates for the other current products have been released. New firmware for the 508 products is now in test, and/or should be available now. I suggest opening a ticket with OBi support at Polycom and ask them to push the latest version to your device.