How to upgrade the OS of Cisco router 3600 series

I have a 3600 Series router which has an OS of 11.0 version and I want to upgrade it to version 12. Please guide
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Istvan KalmarHead of IT Security Division Commented:

First of all please tell us:

'sh ver' command output
IT-MatrixAuthor Commented:
Router#sh ver            
Cisco Internetwork Operating System Software                                            
IOS (tm) 3600 Software (C3620-I-M), Version 12.2(28), RELEASE SOFTWARE (fc5)                                                                            
Technical Support:                                                   
Copyright (c) 1986-2005 by cisco Systems, Inc.                                              
Compiled Thu 24-Feb-05 16:04 by kellmill                                        
Image text-base: 0x60008930, data-base: 0x60A3E000

ROM: System Bootstrap, Version 11.1(20)AA2, EARLY DEPLOYMENT RELEASE SOFTWARE (f
ROM: 3600 Software (C3620-I-M), Version 12.2(28), RELEASE SOFTWARE (fc5)

Router uptime is 11 minutes
System returned to ROM by power-on
System image file is "flash:c3620-i-mz.122-28.bin"

cisco 3620 (R4700) processor (revision 0x81) with 24576K/8192K bytes of memory.
Processor board ID 28010160
R4700 CPU at 80Mhz, Implementation 33, Rev 1.0
Bridging software.
X.25 software, Version 3.0.0.
2 Ethernet/IEEE 802.3 interface(s)
1 Serial network interface(s)
DRAM configuration is 32 bits wide with parity disabled.
29K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read/Write)

Configuration register is 0x102
Istvan KalmarHead of IT Security Division Commented:
You need to buy FLASH and dram if you want to use newer IOS, why do you want to upgrade?
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IT-MatrixAuthor Commented:

PLease tell me the process of buying Flash and dram i am upgrading it because I can not configure VLAN routing in this version. Also can u tell me something else it has a ethernet port and is not fast eithernet while my switches have all fast eithernet ports wont this be a problem for me if i configure it in network ?
Istvan KalmarHead of IT Security Division Commented:
Hi, this router is a weak router with 10M eth port.... I advise to use L3 switch to route between VLANs!

Please refer this page what ram and flash you need:
IT-MatrixAuthor Commented:
Ok Thanks for the advice can you please recommend a couple of strong routers  I have a network of 100+ in my main branch and 100+ users in sub branches I have almost 20 servers and more than 20 cisco switches the network now is kind of flat but i want to create seperate segments and vlans please recommend some good router models
Istvan KalmarHead of IT Security Division Commented:

I advise CISCO 3750 switches, SMI images supports L3 routing with RIP protocoll, if you want to use BGP or OSPF you need EMI image! Don't forget that the L3 switches not support NAT functions!

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