Download the new RouterOS 5.22 release over the torrent network: http://www.mikrotik.com/download/routeros-ALL-5.22.torrent
Otherwise please visit http://www.mikrotik.com/download to pick exact version!
5.22 changelog:
*) userman - fix PayPal "bad HTTP response";
*) kvm - fixed possible ROS guest incomplete package installation;
*) l2tp server - added keepalive-timeout setting;
*) wireless - fixed RADIUS mac-caching;
*) wireless - fixed rare nv2 link stall;
*) metarouter - fixed system occasional lockup for 12s on RB4xx and RB7xx;
*) metarouter - fixed crash when FPU exception was raised in one of powerpc metarouters;
*) quickset - added HomeAP mode;
*) fixed "export compact" in "ip proxy";