Applying a major upgrade between 12.x and 15.x code, backup your config first before go ahead!
Checking the actual version
Cisco IOS Software, CBS30X0 Software (CBS30X0-LANBASEK9-M), Version 12.2(35)SE, RELEASE SOFTWARE (fc2)SW01#show boot
BOOT path-list : flash:cbs30x0-lanbase-mz.122-35.SE/cbs30x0-lanbase-mz.122-35.SE.bin
Config file : flash:/config.text
Private Config file : flash:/private-config.text
Enable Break : no
Manual Boot : no
HELPER path-list :
Auto upgrade : yes
Auto upgrade path :
Downloading and extracting the TAR file from your TFTP
SW01#download-sw tftp:10.1.0.103/cbs30x0-ipbase-tar.150-2.SE6.tar
Loading cbs30x0-ipbase-tar.150-2.SE6.tar from 10.1.0.103 (via FastEthernet0): !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!(omitted for brevity)
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
[OK – 15073280 bytes]
Loading cbs30x0-ipbase-tar.150-2.SE6.tar from 10.1.0.103 (via FastEthernet0): !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!(omitted for brevity)
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
examining image…
extracting info (107 bytes)
extracting cbs30x0-ipbase-mz.150-2.SE6/info (372 bytes)
extracting info (107 bytes)
Stacking Version Number: 1.49
System Type: 0x00000000
Ios Image File Size: 0x00BEF200
Total Image File Size: 0x00E60200
Minimum Dram required: 0x08000000
Image Suffix: ipbase-150-2.SE6
Image Directory: cbs30x0-ipbase-mz.150-2.SE6
Image Name: cbs30x0-ipbase-mz.150-2.SE6.bin
Image Feature: IP|LAYER_3|MIN_DRAM_MEG=128
Old image for switch 1: unknown
Extracting images from archive into flash…
cbs30x0-ipbase-mz.150-2.SE6/ (directory)
extracting cbs30x0-ipbase-mz.150-2.SE6/info (372 bytes)
cbs30x0-ipbase-mz.150-2.SE6/html/ (directory)
extracting cbs30x0-ipbase-mz.150-2.SE6/html/frmwrkResource.htm (950 bytes)
extracting cbs30x0-ipbase-mz.150-2.SE6/html/menu.shtml (8324 bytes)
extracting cbs30x0-ipbase-mz.150-2.SE6/html/portstats.js (8142 bytes)
(omitted for brevity)
extracting cbs30x0-ipbase-mz.150-2.SE6/cbs30x0-ipbase-mz.150-2.SE6.bin (12505683 bytes)
extracting info (107 bytes)
Installing (renaming): `flash:update/cbs30x0-ipbase-mz.150-2.SE6′ ->
`flash:cbs30x0-ipbase-mz.150-2.SE6′
New software image installed in flash:cbs30x0-ipbase-mz.150-2.SE6
All software images installed.
Boot updated with the new image & Reboot
BOOT path-list : flash:cbs30x0-ipbase-mz.150-2.SE6/cbs30x0-ipbase-mz.150-2.SE6.bin
Config file : flash:/config.text
Private Config file : flash:/private-config.text
Enable Break : no
Manual Boot : no
HELPER path-list :
Auto upgrade : yes
Auto upgrade path :SW01#reload
Proceed with reload? [confirm]
New code is Live!
Cisco IOS Software, CBS30X0 Software (CBS30X0-IPBASE-M), Version 15.0(2)SE6, RELEASE SOFTWARE (fc2)
Compare the running config with the Backup one we did previously zero differences, so another successful upgrade!