3750#archive download-sw ?
  /destination-system  specify destination system to receive software
  /force-reload        Unconditionally reload system after successful sw
                       upgrade
  /imageonly           Load only the IOS image(s)
  /leave-old-sw        Leave old sw installed after successful sw upgrade
  /no-set-boot         Don't set BOOT -- leave existing boot config alone
  /no-version-check    skip version check that prevents incompatible image
                       install
  /only-system-type    specify individual system type to be updated
  /overwrite           OK to overwrite an existing image
  /reload              Reload system (if no unsaved config changes) after
                       successful sw upgrade
  /safe                Always load before deleting old version
  flash1:              Image file
  flash2:              Image file
  flash:               Image file
  ftp:                 Image file
  rcp:                 Image file
  tftp:                Image file

This example shows the command in use and the switch output during the upload process:

3750#archive download-sw /overwrite /reload tftp://11.11.11.11/c3750-i5-tar.122-20.SE.tar

使用以下方法可直接将tftp的.tar文件解压至flash中。

Extracting a tar File
To extract a tar file into a directory on the flash file system, use this privileged EXEC command:
archive tar /xtract source-url flash:/file-url [dir/file...]
For source-url, specify the source URL alias for the local file system. These options are supported:
•For the local flash file system, the syntax is
flash:
•For the FTP, the syntax is 
ftp:[[//username[:password]@location]/directory]/tar-filename.tar
•For the RCP, the syntax is 
rcp:[[//username@location]/directory]/tar-filename.tar
•For the TFTP, the syntax is 
tftp:[[//location]/directory]/tar-filename.tar
The tar-filename.tar is the tar file from which to extract files.
For flash:/file-url [dir/file...], specify the location on the local flash file system into which the tar file is extracted. Use the dir/file... option to specify an optional list of files or directories within the tar file to be extracted. If none are specified, all files and directories are extracted.
This example shows how to extract the contents of a tar file located on the TFTP server at 172.20.10.30. This command extracts just the new-configs directory into the root directory on the local flash file system. The remaining files in the saved.tar file are ignored.
Switch# archive tar /xtract tftp://172.20.10.30/saved.tar flash:/new-configs
完成后可使用dir命令去确认一下是否成功。
 
最后记得用boot system命令指定重启后要加载的IOS文件即可。