It seems highly unlikely to me that you could go to a spindle with an R8 taper, if that's what you meant, from another type, unless the machine is designed for that in the first place. But no need to worry. Enjoy yours for what it can do. It'll probably be fine with lighter work and aluminum, just go slow and easy.
added: I should also say that whereas there does not seem to be a drawbar visible on top of the device, it is also possible that it'd be reachable under the cover. Have a look. Between that and looking at the quill/spindle you should be able to tell what's there, if you can't find the manual.
added 2: well, guessing only gets us so far so I finally looked it up as I was curious. The manual specs for that p/n states that the spindle taper is indeed MT-2. That is typical for a (better) drill press. So going to R8 seems like a distant possibility. Now, there are some collets (like the ERs) that have a MT taper shaft and could be used, but realistically, the holding power for side milling is likely to be not so good without a drawbar. Maybe you could add a drawbar to solve that problem if the spindle is hollow, but that seems also unlikely. Check. (I remember seeing an old video by AVE where he used superglue to hold an MT taper in place but would not recommend...

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Then again, a plain MT-2 adapter is probably what you are using now with the chuck, so using an ER - MT adapter would likely be as good -holding wise- as what you have now and would likely be much better for more accurate milling. But more $$. I say keep playing with the chuck until you're frustrated.