Load the new IOS.

Router#config terminal

Router(config)#config-reg 0x2101

Router(config)#exit

Router#reload

Wait for the router to reboot, then reconnect. Once you're back online, re-enter the enable mode.

Router>enable

Router#copy tftp flash

Address or name of remote host [255.255.255.255]? 10.10.1.2

Source file name? igs-j-l.120

Destination file name [igs-j-l.120]?  igs-j-l.120

Accessing file ' igs-j-l.120' on 172.16.101.101...

Loading igs-j-l.120 from 10.10.1.2 (via Ethernet0): ! [OK]

Erase flash device before writing? [confirm] y

Flash contains files. Are you sure you want to erase? [confirm] y

Copy ' igs-j-l.120' from server

 as 'igs-j-l.120' into Flash WITH erase? [yes/no] yes

Erasing device... eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee...erased

Loading file1 from 10.10.1.2 (via Ethernet0): !

[OK - 6070088  bytes]

Verifying checksum... OK (0x14x4)

Flash copy took 0:00:31 [hh:mm:ss]

Now undo the configuration register.

Router#config terminal

Router(config)#config-reg 0x2102

Router(config)#exit

To abort TFTP, type Ctrl-Shift-^ then x.