I meant will my other devices be able to find the "new network, which as I understand, I will have to let it find it by entering the new name
Devices will not automatically "find" the network. If you have a Mac, for example, you will have to click on the WiFi menu at the top of the Mac's screen to "see" the new network. Then, click directly on the name of the network to select it. If you are asked to enter the password, type it in.
Is it only the Express that will need to be reset,
Yes, since you will have already edited the settings on the AirPort Extreme.
how would I do it with the Express?
With the Express powered on, hold in the reset button on the Express for 7-8 seconds and release. Allow a minute for the Express to restart to a slow, blinking amber light status.
Click the WiFi menu at the top of the Mac's screen and click directly on AirPort Express under the listing of New AirPort Base Station.

When you click on AirPort Express, that will activate the setup "wizard" to help you with the setup....like the example below. Follow the prompts to assign a device name to the Express.....(you can use the same device name that you used before).....then click Next and the wizard will set up things automatically.
