No need to update firmware for your uses. You can if you want but not likely to change anything for you that is important.
Just a note... since you say you are new to GMRS and Radio...
Unless the other coaches are your family relatives, each one of you legally should get your own individual GMRS licenses. If they are family you can share, if not each person is licensed, not the radios. Another alternative, if the others use FRS radios (which use the same frequencies/channels as GMRS) but are lower power), they would not have to be licensed (FRS is a no license required service). You would be able to use your GMRS radio to communicate with FRS radios, and your family could use your GMRS radios with your callsign.
Besides this, if you are only communicating from one side of the athletic field to the other, you probably don't need anything more powerful than FRS.