Hm.. going to Updater app and hit Menu button and then Reboot to recovery.
This is how you install roms, do wipe etc.
I think you should read before doing something because I think you have zero knowledge about MIUI or custom roms.
You have very old MIUI and want to change with one of the newest roms from MIUI v5 base. This requires full wipe of your device. So you would need to backup all your data and format /system before installing new MIUI.