Download the new RouterOS 6.8 release over the torrent network: http://www.mikrotik.com/download/routeros-ALL-6.8.torrent
Otherwise please visit http://www.mikrotik.com/download to pick exact version!

6.8 changelog:

*) bridge - default protocol-mode changed to RSTP for new bridges, fixed bridge mac address changing when port (with lowest mac address) goes down
*) userman - improve startup time;
*) sstp client - support server name verification from certificate;
*) wireless - improved 11n and nv2 stability;
*) dhcp client - support interfaces in bridge;
*) dhcp - parse decimal strings and IP addreses in options value;
*) bgp - don't show community 'internet' in BGP advertisements;
*) ipsec - enable hardware acceleration for aes-cbc + md5|sha1|sha256 aead on tilera cpus;
*) ospf - fixed checksum calculation for OSPFv3 AS-external-LSAs;
*) default configuration - changed dhcp server lease time to 10 minutes;
*) fixed port isolation on CRSs (bug introduced in v6.6);
*) smb - added support for SMB 2.002
*) timezone information updated;
*) ppp - fixed ppp bridging (did not work since v6.6);
*) improved speed of PPP, PPPoE, PPTP & L2TP on multicore routers;
*) address-list - fix crash when adding two identical address list entries (not allowed any more);
*) fixed multicast forwarding on CCRs;
*) firewall - improved address-type matcher, and added it for ipv6 aswell;