Sadly, the Flash storage is soldered and not really replaceable by most. There are a few techs that have the skills and access to the parts. I’ll warn you it’s not cheap and your current stuff won’t be accessible so you’ll want to do a full back up before anyone does anything.
Frankly, buying a used/pre owned system which meets your needs and then sell yours is the best way. But you’ll need to need to float the cost until you sell yours.
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