Benoit Verove take a closer look, it's just update from Gaia R77.20 to Gaia R77.30.
So, you want to upgrade something with Check Point software? Then the first thing to do is to go to Upgrade Wizard and put in there your current and planned hardware and software.
For your situation you will find the same package that you already mentioned - Check_Point_R77.30_T204.Gaia.tgz
Create a snapshot and copy it somewhere safe.
Copy this upgrade file to the server to somewhere in /var/log/ directory, run tar zxvf on it and then ./UnixInstallScript
After that update CPUSE and install the latest Jumbo Hotfix Accumulator (General Availability).
I did this several times recently on Smart-1 management servers (MDS), gateway appliances and on VMs.
If you have some old hotfixes, upgrade might not start. Or Jumbo Hotfix might conflict with them. So, you just delete them. But if you have some case of a special hotfix for you unique situation, it would be better to verify with TAC that this is included in upgrade or Jumbo Hotfix, or to ask for this hotfix for the new version.