FRS and GMRS are two separate services. However, they share some frequencies.
FRS is a 22-channel service that only allows for 2W on 1-7 and 15-22, and .5W on 8-14. You cannot use a detachable antenna. You cannot operate through repeaters. It is license-by-rule with no call sign requirement.
GMRS is a different service that shares 14 of its channels with FRS (in FRS they are numbered 1-7 and 15-22). GMRS rules are different from FRS, in that GMRS allows for higher power, detacheable antennas, base/mobile radios, and repeater operation. It requires an explicit license and call sign.
For two decades, FRS was only a 14-channel, .5W ERP service which shared channels 1-7 with GMRS (but still only at .5W). In the early 2000's the FCC allowed manufacturers to build radios that included both GMRS and FRS type acceptance, which opened the manufacturers to using 22 channels, adding higher power channels 15-22 and allowing for higher power on 1-7. Since 8-14 were FRS-only service frequencies, they were still limited to .5W ERP. However, to legally use channels 1-7 or 15-22, the user was supposed to get a GMRS license and only use channels 8-14 if they did not have a GMRS license. Virtually all "FRS" radios on the market, today, were built under those rules, so the packaging, manuals, etc are somewhat confusing, as they are no longer in sync with the actual rules, which changed a couple of years ago.
The FCC now forbids the combination of license-by-rule service and explicit license service channels in a single radio. However, at the same time, they expanded FRS from 14 to 22 channels and codified the rules to match what was actually being built. I had a lot to do with proposing and promoting this form of the changes, including 3 face-to-face meetings with both the technical and legal groups at the FCC in D. C.
Later this year, all "grandfathered" radios will have to have new FCC grants that are single-service, FRS-only grants rather than the dual-service grants they have today.
GMRS does not and has never included FRS channels 8-14. You cannot legally operate on those frequencies on anything other than a radio that has type acceptance for FRS as reflected in the radio's FCC grant.