For best results, recipes should typically either be cut in half, or doubled.  In other words, if the original recipe serves 6 but you want to make a smaller quantity, your best results will be if you change the serving size to 3.  Or, change it to 12 if you want more.  This is because not all measurements can easily be converted to other serving sizes.  For example, if one ingredient in a recipe that serves 4 is 1/4 cup sugar - it's easy to cut that in half (converting that same recipe to serve 2 people instead), to 1/8 cup of sugar.  But if you try to change the serving size to 3 (instead of cutting it in half) that 1/4 cup of sugar becomes 0.188 cup.  That's not to say you can't still convert recipes to other serving sizes, you just will have to do a little extra figuring on your own to interpret the measurements.