FortiGate 40C - How to menage the Partition?

[Cappej]

Hi you all!

I've just updated to 5.0 patch10 (build 0305) from a V4

if I use the command in the CLI:

diag sys flash list

I'll receive:

Partition Image TotalSize(KB) Used(KB) Use% Active

1 FGT40C-5.00-FW-build305-141216 128979 24305 19% Yes 

2 FGT40C-4.00-FW-build689-140731 128979 19114 15% No 

3 ETDB-16.00432 3586560 82832 2% No 

Image build at Dec 16 2014 17:44:18 for b0305

I've complete many test and my new upgrade is fully function, so I would like to format my 2nd partition with old firmware to install the new 5.2 or 5.4 'cause I want to test the "Virtual WAN" service.

Obviously, my first-rock-solid partition n.1 will be present until the end of the test of the newer...

FINALLY... THE QUESTION:

1) What is the right way? in UI I don't find noting to amin the partition and I want to be sure to emit every any damage to my partition n.1 (I've got the backup config)

2) How can I boot from the 2 partitions (for example reboot from n.1 to n.2 and viceversa)? 

I accept an "HOW TO" or any guide... I'm not able to find nothing about it.

Thank a lot

Marco (Italy)