Hi Guys,
Just to let you know that everything went OK. It was like an LTM upgrade, as you suggested. The controllers' disk-formatting scheme were already volumes so I just had to install online (stby unit) and then boot in the installed partition. After the big-ip went up it took like 5 minutes to load ASM module.I noticed that when I clicked the ASM>Overview menu and got something like BIG-IP ASM wasn't loaded. Almost died but it was only a matter of time to get things work perfect.
Thanks everybody again for the support!!!
HH