What does your current bass do that you wish it did differently?
…And also: what does your currend bass not do that you wish it did?
^^^^These
"Upgrade" is a bit of a nebulous and subjective word.
The Yamaha TRBX is a great bass. Just because another bass costs more doesn't mean it's an "upgrade". It's just a more expensive bass. For it to be an upgrade it needs to do something
better than the one you have,
for you. And "better" is a completely subjective term. You need to specify where your bass comes up short, what problems you're having with it, and what it doesn't do that you wish it did to know what other bass will actually be an "upgrade,"
for you.
Almost everything on your bass can be adjusted tone-wise. Different strings + EQ will do the most tonal change for almost no money. Differently voiced pickups could change the tone too, without buying a whole other bass. If your bass has issues staying in tune, you can buy new tuners. If the bridge isn't holding string height or intonation, you can replace the bridge.
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None of this is to say "don't buy another bass." Always buy more basses.

But don't necessarily think of it as an upgrade unless you're actually solving problems you have with your current bass, which goes back to the two questions by @urkel3000 and @JakobT
Otherwise, just start looking at whatever basses that strike your fancy.