Welcome to the forum.
From what I see by doing a search on that filter you need to remove the collar to take the entire valve assembly off the filter. Sounds like you already got the collar off. The 6 screws you mention are for the valve assembly itself, to take it apart. That collar I mention scrunches the valve assembly to the filter body. Since you already have the pipes removed, once that collar is removed the valve assembly should lift off the filter body. Probably just stuck so try twisting it. No threads or anything magic. Looks like the Hayward filter I have.
Even after 7 years there should be no reason to replace the sand. I'm on the 9th season. Only reasons to replace sand should be if you really gunked it up somehow, you suspect damage to the laterals or other components inside the filter, or you suspect the wrong kind of sand was used last time it was replaced.
I'm not familiar with that specific filter so if anyone has more info please chime in.
Al
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