The name of the package will likely vary from distribution to distribution. It's difficult to give a specific answer to a general question but generally, the easiest way is going to be to install from the distributions repositories using either their graphical package management interface (if they have one) or the command line.
The RT5370 is ralink. So generally just install ralink firmware
For instance if you are on Debian/Debian-based distro (or, more accurately, your distro uses dpkg/apt-get) just
Code:
apt-get update && apt-get install firmware-ralink
should get you going