1、配置好TFTP服务器（假设ip为192.168.2.1）
2、查看当前IOS名称
#show version
输出中有一段：System image file is "bootflash:/isr4300-universalk9.03.16.05.S.155-3.S5-ext.SPA.bin"
IOS名称即为：isr4300-universalk9.03.16.05.S.155-3.S5-ext.SPA.bin
3、复制IOS到TFTP
#copy flash: tftp:
//分别填写下面的信息，Destination filename不用修改，直接回车即可
Source filename []? isr4300-universalk9.03.16.05.S.155-3.S5-ext.SPA.bin
Address or name of remote host []? 192.168.2.2
Destination filename [isr4300-universalk9.03.16.05.S.155-3.S5-ext.SPA.bin]?