Download the new RouterOS 6.15 release over the torrent network: http://www.mikrotik.com/download/routeros-ALL-6.15.torrent
Otherwise please visit http://www.mikrotik.com/download to pick exact version!

6.15 changelog:

*) fixed upgrade from v5 - on first boot all the optional packages were disabled;
*) fixed problem where sntp server could not be specified in winbox & webfig;
*) metarouter - make openwrt work on ppc metarouter again;