DON'T change the pickup! Trust me, it won't make much of a difference.
The pickup itself is one of the least important factors in a Stingray (and most active basses in general). As long as it's positioned properly and it's a good-quality pickup (which it is if you have a MM Stingray) then just leave it be.
Here's 4 things that will have a much higher impact on your tone (and 2 of them don't cost money):
1) Adjust the pickup height - Stingray's are known for having a HUGE E and A string but then lack something in the other 2, especially the 2-band Stingrays. You can lower the "bass" side of the pickup or increase the "treble" side of the pickup (or both if you want to)
2) Adjust your action - Stingray's are very sensitive if you have a lower action. Since it's a HIGH clarity bass, everything you do will be heard - that includes fret buzzing. Me personally I love the Stingray's slight fret buzzing when digging in, it seems "ugly" solo but in a mix it really gives you that attack to punch through. But some people might not like it. So adjust your action accordingly.
3) Change your strings - as I said, the Stingray's are a high clarity bass that really reflect everything you put on them, moreso than most basses. Strings are essential to get the sound you're looking for in your 'Ray. Now it all depends on what tone you want, I'd need more info, but strings really make a HUGE difference on the Stingray bass.
4) Change the preamp - last resort option, if none of the 3 above work for you, a preamp change will have a much bigger impact on your tone than a pickup change. There's plenty of preamp options around and all of them are slightly different.
p.s: this goes without saying on active basses, but make sure the battery is working fine. if it's not, you'll hear it - your bass volume will be much lower and even when you're playing clean your tone will sound like it's distorted.