How far ‘out of range’?
If a different (better) antenna will make any difference depends on different factors, like distance, antenna placement, obstacles etc.
You may possibly need to setup your own indoor or outdoor gateway.
Improvements are possible but depend on different factors, one being the antenna’s included with your Heltec boards. You have not given any details about your antennas. The type of antenna’s included will depend on region and probably on time of production, time and location of purchase and availability.
Also have a look at:
If you want to do and learn anything more than just running someone else’s sketch then reading documentation and learning the essentials will be useful.
This topic (start at the top) and other topics on the forum contain useful information to help getting you started.