Your university's writing center should be pretty up-to-date with style guide editions (if you have a question, you could probably ask them and they would most likely be able to answer it for you).
Also, Purdue Owl is generally up-to-date and update when new editions come out (usually within a few months of the guide's copyright date), so you can search the on their website the style your using.
Your university book store also should have new editions of style guides (however, this can vary from university to university), which you can purchase.
Usually, styles have blogs that are pretty helpful when new editions come out (e.g., APA: https://apastyle.apa.org/blog). Just search MLA/APA/etc. style blog in google to find them.
Also, whenever a new edition of a style guide comes out, professors and institutions have a grace period where they can chose to either use the current or previous edition (e.g., when APA 7 came out in 2019, there was a grace period til late 2019/early 2020 where professors and institutions could chose to either abide by APA 6 or APA 7). but it's always good to check with your professor/institution on this as the "grace period" is not wholly set in stone.