Afraid to update software in case I can no longer download non-Amazon books

Hello all.

I have a Kindle running software version 5.16.9. I typically leave my Kindle on airplane mode just to conserve battery. I've read some information online that one of the software updates caused people to be unable to download books to their Kindle that they did NOT get from Amazon. I get pretty much all of my books from non-Amazon sources so this has me pretty worried.

Should I be okay to update my software, or is it going to cause problems?