multiple versions of Mongo

multiple versions of Mongo

When I start the mongo shell from
~/Downloads/mongodb-osx-x86_64-2.4.5/bin, it starts up version 2.4.5
./mongo
MongoDB shell version: 2.4.5
That's the version I just downloaded.However, when I run the mongo command
from anywhere else in my terminal it starts a different version. I think
this is because I (obviously) installed Mongo previously.
MongoDB shell version: 2.2.0
connecting to: test
What do I need to do to make 2.4.5 respond to 'mongo' from anywhere in the
terminal (i.e. to replace 2.2.0 with 2.4.5)