If you go to Control Panel -> Administrative Tools -> Computer Management, you can select the Storage | Disk Management node of the tree on the left, and that will display all of your physical drives, including the removable ones that are currently installed.   If you right click on any of those drives, you can  "assign a drive letter".    Likely, to assign a drive that is "K" to a lower letter, you will have to assign the drive that has the desired lower letter to "L" or something, in order to free the letter up.

Smartass answer:  Refuse to run any software with that kind of a drive letter limitation :)   Sorry... couldn't resist.

I find it interesting that on my laptop, there is no "J:" or "K:" drive, until I insert a card (SD card becomes J: and PCMCIA becomes K:).   However, on my desktops, that have four built in card readers, they all get a drive letter, whether there is a card in them or not.   And, then you insert a card and are left guessing which of the four might match the card type that was inserted.   Of course I play hunt the wumpus until I find the right one, but forget to rename them or anything to avoid the problem the next time (as one desktop doesn't use the same mapping as the other desktop). 

As to why one card shows as removable, and the other doesn't, I can't answer that question.  I've seen it too.    But it never impacted me getting done what I wanted to do, so I just drove on and hoped that onday Ed or Van would provide a little FTTKAT in that area.

Good luck!