OK, i have just picked up (like 5mins ago) a free bike, its a Malvern Star Sprint 12, girls frame...

the gearing is shimano RS

my question is can i swap the rear cassette onto my road bike (unknown brand, but has 6 speed shimano 600 rear cluster at the moment) as my current gearing is stupid silly for going uphills (42-18 is my lowest gearing) the one on the new free bike looks like a much wider range....

hoping you can help!