Pathfinder Character Sheet help

I am completely new to Pahfinder/DnD and Tabletop games in general but i started DMing for some friends my problem is that when we put in ability scores the wrong modifier comes up. for example if we put 18 in strength 4 comes up in modifier. but in the core rulebook it says 17 should come up. (we roll for stats if that helps) I found out that this is the purchase system but we would like to use the Dice system. how do i Change the sheet to dice system? am i missing something obvious?

I am sorry but i think you are misreading the core rulebook. Ability Scores and their effective mods are as follows: 6 = -2, 7 = -2, 8 = -1, 9 = -1, 10 = +0, 11 = +0, 12 = +1, 13 = +1, 14 = +2, 15 = +2, 16 = +3, 17 = +3, 18 = +4, 19 = +4, 20 = +5, 21 = +5, 22 = +6, 23 = +6, etc.

Hi Roy. There isn't a right/wrong way to figure ability scores. There are many methods, some more common than others. <a href="http://www.d20pfsrd.com/basics-ability-scores/abil" rel="nofollow">http://www.d20pfsrd.com/basics-ability-scores/abil</a>... It's up to the DM/group. That said, Simon is correct in listing what the modifier would be given the appropriate ability score. The Pathfinder sheet uses a formula to calculate the modifier. It doesn't care how you derive at the ability score(dice, point-buy, thin-air, etc.) e.g STR-mod ((floor(@{STR}/2)-5) + floor(@{STR-temp}/2) - (floor(abs(@{STR-damage})/2)) - (floor(abs(@{STR-penalty})/2)) - [[ @{condition-fatigued} ]])