[Koha] put on hold a book

i want to put on hold a book but i receive the message Cannot place hold - *Too many holds: *Witness Kalomo <http://www.opac.mlrc.saut.ac.tz:8080/cgi-bin/koha/members/moremember.pl?borrowernumber=51>has too many holds. but it allow me to hold a book ,how to remove the book -- regina