update cisco ios

sir..
i got new cisco IOS mu current ios dtls given below (C2800NM-IPBASE-M), Version 12.4(3i), RELEASE SOFTWARE (fc2),c2800nm-ipbase-mz.124-3i.bin my new file name is c2800nm-ipbase-mz.124-24.T.bin its i did download to my pc
i want to change my IOS can u help me how to do
step by step please …?