I was looking at the picture of cactus and am wondering if its actually one one those plants, that looks like a cactus but doesn't actually belong to cactus family, especially as you said it grew quickly. So as your photo is a little dark and I can't quite see your plant properly, am posting a picture, to ask you if in real life - does your plant look like this one, which is a Euphorbia rather than a cactus but is commonly known as a Candalabra Cactus
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These plants although not a true cactus are succulents, so in terms of re- potting they are treated in exactly the same way. They grow best if re potted every two years and this is best done during the active growing season which is late spring or early summer, so I wouldn't advise you to do it now, unless it is totally root bound and you have lots of roots coming out of the bottom,and the plant appears to ailing because of it.
When re-potting you will need to water the plant two days prior to doing it and once re- potted don't water immediately, but wait at least one to two weeks before doing so. you will also need to make sure that you give it plenty of drainage, by choosing a sandy or gritty based compost and placing crocks, pebbles or small rocks in the bottom of the pot, plus make sure that the new pot has adequate drainage holes in the bottom.
You are unlikely to kill your plant as they are pretty hard to kill and if you should accidentally break some of it, it will soon grow again and you can always use the broken piece to propagate another by placing it in some dry soil.
Everything I've mentioned applies to both succulent and cactus plants, so whichever type of plant yours is, this has hopefully solved your dilemma