Turn off the machine, turn off power supply (if possible), ground your self by touching the metal of your case or power supply and install the card. I usually lay the case in its side but it's up to you.
There is likely a tab on the PCIe that sort of "locks" your GPU into place. Make sure you release this tab, otherwise you'll break it pulling your card out. The slot is still usable, but the tab helps to make sure everything is locked in place.
The ones on my Asrock board were pretty small and I was irate trying to fix a problem one night, and broke the tab on the PCIe slot my card was plugged into. I was afraid I had broken something, but fortunately the slot and everything else still works (and has for a year now).
Just saving you from a mini heart attack and thinking you broke something like I did.
Otherwise follow the rest of the advice you've been given. Swapping cards is very easy overall.
Also, if you're switching brands, make sure to fully clear your system of the old drivers before installing the drivers for the new brand of card.