Cannot update Wordpress version for my users

Hi. I have a VPS with GoDaddy, WHM and 14 accounts (they are all mine). 2 months ago, I installed Wordpress for each and every account from their cPanel. Back then, the version was 3.9. Now I want to update them all to 4.0, but Wordpress won't offer me to update. I also tried to do that from WHM (see image whm-1), but I get (see image whm-2) "Requires MySQL 5 or newer. Could not prepare working directory: No such file or directory". I have MySQL 5.5.37 installed. Any suggestions? Thanks!