If this is really what you are doing, you don't seem to have any grasp of how gears are used or what "direction" to shift in as speed and terrain vary. It's also possible that you are using the terms "cassette" and "chain ring" incorrectly since reversing them in your description makes more sense. The cassette is the cluster of multiple cogs at the rear wheel and the chain rings are attached to the crank.

The largest chainring coupled with the smallest rear cog is the potentially fastest but hardest gear combination and is usually used only for downhills and/or with a strong tailwind. As you shift to larger cogs in back or to a smaller chainring, the bike goes slower at the same pedaling cadence (spin rate) but the effort gets easier. Large cogs and small chainrings are used to climb hills and fight headwinds.