Hello, first time plant owner here. I noticed today that my cactus's roots have emerged from the drainage holes in the bottom of the pot (see image). I read online this means it is time to re-pot my cactus, but I just got it a few weeks ago, and I also read online you don't need to re pot cactus's often because they like small spaces, and my cactus is still pretty small, maybe 6in. tall? (see image). So, I was wondering, what should I do? Do I need to put it in a bigger pot already? Thanks in advance.

Hi & welcome!

Requesting to move this to cacti/succulent forum where those who know this plant well would be most likely to see your question.

If the roots are coming out the bottom, the plant is telling you it wants more space. There's no need for a huge pot at this point, just bump up the size one notch and observe from there on out. Maybe an inch wider and half an inch deeper would be good. When you repot, try to use soil with good drainage (with maybe 50% rock=pumice, perlite or equivalent) and avoid a very deep pot. It's probably better to repot sort of regularly in smaller steps than make big leaps all at once. Avoid watering immediately after repotting, especially if you damage the roots during the process. After a few days there should be no need for concern.

If you just bought it, it may still be in soil that is not ideal for cactuses. What I do when I buy cactuses from big box stores is to remove them from the pot, remove as much of that dreaded peaty soil as I can to get them bare root, then trim the tips of the roots. I let it rest for a couple days in shade all naked like that, then repot with proper cactus soil amended with pumice. Then gradually introduce back to sunlight. Also don't water for at least a week if not longer.

Your cactus is not a cactus. It is a Euphorbia and needs to be grown like a succulent. Do not over-water.
The roots are telling you that it is time to re-pot. Move it up to the next size larger pot, can be deeper since these guys like to grow fast. You do not need to trim the root tips; however, they will probably have some damage from re-potting, so do not water for few days to give it time to heal. Euphorbias do like full sun so give it plenty of light. Post another photo when it gets bigger and we might be able to give you a name for it.