Epubor works great. I've used it for 6-8 years....couple versions. On laptop.
Able to convert multiple formats, epub, azw, mobi,,text, pdf. Check site out.
You drag & drop your Amazon Kindle e-books into the box, .AZW or.MOBI
1) Epubor reviews the book or books, removes digital rights management.
2) You choose what type of format you want to use, .ePub, push Convert button, and in 10-15 seconds, done.
3) Transfer your .ePub copy into your filing folder. Done, Rename it your way.
4) When done with Epubor, delete all books in the Ultimate folder, then delete your .AZW or .MOBI books. You won't need them anymore
Note: I save my books in .ePub format because 85-90% of the world uses it. And it's free. My .pdf files, I keep as .pdf
The .ePub format takes up way less space on your hard drive compared to .mobi, or .azw.
And make sure you have a filing/renaming system of storing your e-books.
And the biggest storage device you can afford, I have somewhere between 1-2 terabytes at this time and it will only go up.
I believe that for the Kindle readers, you can now read .epub books on the newer Kindles.