How to increase wireless speed?

Hello,

I am currently using Pi Zero W with latest PirateBox 1.1.3 version. My upload and download speed from the Pi is not satisfying so what I would like to know is, if it is possible to increase the speed? will adding an antenna only increase the signal or also speed? Also like can I use wireless AC USB dongle? Is there a guide for that cause I cant seem to find it.

Thanks devs for PirateBox!! Greetings!! :)-D