I am about to upgrade a web server from pi2b to pi3b. I would like to know if I can take the SD card as it is from the Pi2b and use It in the pi3b, and the higher performance options for the pi3b be recognized? I really don't want to start a fresh install for the pi3b and transfer the Web site if I don't have to. Distro is raspbian Jessie. Thanks yall
Yes - provided the OS is new enough. You don't say what OS you are using. Assuming Raspbian Jessie you need kernel
4.1.18 or later.
To be on the safe side to a
sudo apt-get update followed by
sudo apt-get upgrade first.
I would recommend
sudo apt-get dist-update which will get the latest, released a few days ago. This has some useful additions, but you will need to install extra packages to get all of these see https://www.raspberrypi.org/blog/#another-update-raspbian