It's really easy. First cut the old strings. They should come out somewhere through holes in the back of your guitar (the holes are behind a cover shield but you don't need to remove that). In those holes you put the new strings, and tighten them to the tuners (you should remove the old strings from the tuner first). Then you need to tune your guitar. The first time you do it it will take you a lot of time, but if you do it often it goes really easy.
Just give it a try ;-)