Hiya tastolz n welcome to the party!!!
What size are you knitting? the first size or small you decrease 5 stitches evenly across the purl row. medium, decrease one stitch, large; decrease 1 stitch and extra large decrease 5 stitches.
Now to explain the evenly across thingee, you are going to spread out you decreases across the row so that they aren't all bunched toghether in one spot.
The formula for how many stitches between the decreases goes something like this:
take the total amount of stitches and divide them by the total number of decreases in that row, the answer you come up with is how many stitches between decreases.
In your case it would be 93 /5 = 18.6 so you would do your first decrease on the 8th and 9th stitch and then on each 18th stitch after that. It won't be perfectly symetrical but it does evenly space out the decreases. You would do the same formula for increases as well.
Hope that helps ya hun.