How can I strengthen my wifi when in a public location?

I heard there was a way to hack the network or something idk....

Rather than trying some illegal manipulation of the other person's software, why not try some perfectly legitimate tweaks of your own hardware?

Wireless antennas usually send signal equally in all directions. This is handy if you don't know where it ought to be aimed, but it wastes power by sending most of the signal in the wrong direction. You can boost your computer's signal strength by using an antenna that only points in one direction.

Here is a contest-winning design:
https://www.instructables.com/id/Uni-Directional-WIFI-Range-Extender/

And a number of others:
https://www.instructables.com/tag/?q=wifi+boost&limit:type:id=on
^^Seconded. 

Another thought is just get a wifi card with external antenna - it will likely have better signal strength simply because its not in the computer case.  Another option is get one that you can add a HIGH GAIN antenna which will send and receive signals better - at the cost of bulkier size.
Re-design8 years ago
Find out where their router is and sit as close as you can.