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You can't upgrade a SSD, only replace it with a different one. If R9 allows you to add another SSD, that's probably your best option.
Fyi I have an Aurora R6 with following:
♣ C: 256GB SSD for Win10 OS & a lot of software.
This is deliberately small to make my monthly disk images—just before the monthly MS OS updates—quick and easy, with a verified image in 30 minutes. These images mean if Windows or SSD crash n burn, I can be back up & running in ~30 minutes—proven twice back in '16 when Win10 was still a bit flaky. I recommend Macrium Reflect for this.
SSD is much faster than HDD, and so should contain files which are being used frequently—mainly OS, software installations, and your current game if you don't have a separate games SSD.
♦ D: 4TB HDD for data.
Most personal & work files go here into an organized folder structure. When it got fullish, I moved media files off it onto the external. C:'s images live here too.
Things like documents and photos are only accessed occasionally, so there's little benefit from having them on a fast SSD.
♥ G: 1TB SSD for games.
I don't do much with this drive, no backup because it's not a big deal if it goes bust—just download & install current games again and start afresh, or resume if there's an online save.
I don't play recent games, yet my largest is 130GB. Since my internet isn't great, I picked up this drive to keep games I want to replay. SSD can be a big help for games—always with the launch, sometimes also during play—so it's worth it imo.
♠ External 4TB USB backup drive for minding D:'s data files and latest C: images.
Rarely accessed files—which are over 80% of all data files—can be zipped to save a lot of space.
♣ S: 64GB USB in router for our network needs.
Very handy, since we leave the router on all the time but switch our PCs off—no space consumed, no need to leave other PC on so other person can have access to shared files.
No need to backup since we both have copies of its contents for working on.
♦ Biz server holds backup of vital data—upload speed is too slow for any more—but I'll probably move to using OneDrive 'sometime' soon, since I have it as part of our biz software. There are plenty of free online storage places you can use if you want to.