You need to go
here and download the Amon Ra 2.3 zip and place it on the top level of ypur sd card/not in a folder, also known as root. Rename the file PC36IMG.zip (or no .zip depends on if extensions are shown or not on your pc/phone). Turn off the phone. Turn it on by pressing and holding vol down then pressing power (go to hboot). If named properly and in the correct place it will scan and find the file and ask if you want to update. Say yes, it twill update then ask if you want to reboot, say yes. You should now have amon ra recovery. Rename the PC36IMG file to something else when you are done so it doesnt try to flash it every time you go to hboot.
Clockwork back ups can NOT be restored with Amon Ra, you will need to flash back to clockwork to restore a recovery made in clockwork. Or flash back to that rom first, flash Amon Ra and make a back up of that rom, thereby making amon ra back ups of all your roms, you would have to repeat that procedure for every clockwork back up.
As far as Rom manager is concerned you can keep or uninstall it. It will not do anythingg as far as recovery is concerned but it can still dl roms and fix permissions.
Edit: If you already have the corect file skip going to that link and start at placing it in the proper place and naming correctly.