This is my first iPhone and first apple product. It's amazingly fast and fun. My question is will it become laggy if I download too many apps. Also will having more memory left make the phone faster. I only have a 16gb model.
To restart your iPhone, hold down the top button until the red slider appears, slide it off, press top button for about five seconds, iPhone will turn back on.
It has 512 MB RAM and 16 GB flash memory. The flash memory is used for storage, so no, downloading lots of apps should not slow the phone down.
The only reason to restart the phone is if it seems to be doing something out of the ordinary like being slow or crashing or whatever. I only did that a few times with my 3G.