MAC OS Updating?

[MrKnifey]

Hi guys, just got given an old MAC Computer, my first Apple PC and im a bit lost. Ive gone to sync my iPhone4, its told me I need the latest iTunes. Ive downloaded that but its told me my OS needs updating, im currently on 10.4.11.

Ive had a look on here and the Apple website as to what I need to do to update to 10.5 but, im either being thick or blind but I cant find out what I need to be doing? I take it that it isnt like windows where I just click update? Any help is appreciated.

Thanks

 

[MrKnifey]

Spec is as follows:

2GHZ Intel Core 2 Duo CPU
1gb Ram
160gb HDD

Plus all the usual.. Would Lion 10.7 work?

 

[MrKnifey]

I have some ram out of my old PC.. its DDR etc.. Stupid question, but will it work?