Download the new RouterOS 5.25 release over the torrent network: http://www.mikrotik.com/download/routeros-ALL-5.25.torrent
Otherwise please visit http://www.mikrotik.com/download to pick exact version!
5.25 changelog:
*) web proxy - speed up startup;
*) metarouter - fixed occasional lockups on mipsbe boards;
*) wireless - update required when using small width channel RB2011 RB9xx caveat: update remote end/s before updating AP as both side are required to use new/same version for a link