There are usually notes next to amp binding posts where to connect your speaker wires if the amp is bridged. If not, it's either doesn't matter or you can simply trial-error (only make sure that you don't swap positive and negative) to see where you get your sound louder. Have a mute switch handy or simply switch to dummy source your preamp before each trial. If your speakers are biwireable, you can take an advantage using all 4 binding posts to all 4 binding posts if bridged amp tests same from all terminal pairs.
