It's very easy, just don't use the gears you don't need.

I don't mean to be facetious, but I'm not sure what your objective is. If you simply don't expect to use the low end of the gear range, the innermost chainring (granny) can be removed easily enough (Removing the innermost ring would require removing the crank first) and the front derailleur adjusted accordingly. Or you can leave it in place and simply adjust the FD so it can't be used.

As I said, I don't understand what you hope to achieve, but seeing as you're fairly new to this (based on the question) I suggest you ride it as is until you have a sense of which gears you actually use, then you can make modifications to suit your needs, if required.