You can do it

First, make sure you have the correct GFI outlet. Look at the breaker which feeds the circuit you are working on. As a rule (but not guaranteed), kitchen circuits are 20 amps, and bathroom, garage, and outdoor outlets are 15 amps. The clerk at the hardware store will show you the correct one to buy. Second, shut off the breaker feeding the circuit you are working on. Remove the old outlet and spread the wires out so they don´t touch each other. Turn the breaker back on and, with a circuit tester, determine which set (black and white) of wires is hot. Shut the breaker back off. Install the hot wires into the screw terminals marked LINE. The marking is on the back of the new outlet. It will also be marked to indicate the black terminal and the white terminal. If you have more sets of wires, they will be installed in the terminals marked LOAD. Screw the outlet into the box and turn the breaker back on. Push the reset button to "turn on" the outlet. Push the test button to make sure it is working properly, and then reset and enjoy.