How to downloa gta san andreas on my iphone 3gs?

I have an iPhone 3GS and I have gta san Andreas downloading but when it says downloading it the. Says not enough storage space. I know I have enough exams it only takes 1.6 gb to install. I have exactly 2.5 and it keeps on saying that. Can someone please explain this to me please?

I'm no expert on Apple products, but it may be that it reserves some amount of memory for system purposes. In your case, the problem of Apple phones is they do not support either opening the case (like changing out a battery) nor SD cards. If they did the latter, you could put in a 16 GB SD card and download big games all you want. Ever consider an Android phone for games? More are even FREE.

The vendor should include the necessary information at the site where you bought it.
As said you need more room for game saves over what the initial installation takes.