You can't. The old N-Gage game are intended only for the original N-Gage or N-Gage QD phone. The new N-Gage games require certain S60 3rd Edition based phone models. The N70 is an S60 2nd Edition Feature Pack 3 model, and is not supported.
The list of supported devices for N-Gage, you can get from:
And on a supported phone, before you can run the N-Gage games, you need the N-Gage application, which you can download from the site first, if the phone does not come with it from the factory (for the moment, only the N81 and N81 8GB come with N-Gage preloaded, but I'm sure more models will also start to come with it).