Re-allocate /home on a diff partition

My present harddisk partition info is as follows

[user@dreamer]# df -H
Filesystem Size Used Avail Use% Mounted on
/dev/sda2 86G 2.4G 79G 3% /
/dev/sda7 20G 80M 19G 1% /BACKUP
/dev/sda1 104M 16M 83M 16% /boot
/dev/shm 1.1G 0 1.1G 0% /dev/shm
/dev/sda3 26G 111M 24G 1% /home
/dev/sda5 21G 7.1G 13G 37% /usr

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I plan to have a lot of users on this machine (around 10,000)
As you can see there isnt much empty space in /home partition.
I want to shift the /home folder under ' / '.
ie I want /home also on ' sda2 ' instead of sda3.

Hw do i go about doing that.
Are there any risks involved??

Thanks in advance.

Arun

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