If that's all you are after....
Start out by multiplying every base thing by 10. A level-1 NPC human commoner has 1d4*10 HP, the NPC ability rolls are 3d6*10 in each stat, synergy grants +20, DC's for tasks are multiplied by 10, the d20 on the skill roll is multiplied by 10, you get +10 to one stat every four levels, et cetera. Modifiers are based on the stats as normal, with the exception that the "center line" is 100 (10*10), rather than 10 (so a dex of 110 (roll of 11) gives you a +5 to AC, but it hardly matters, as the attack roll against you is 1d20*10; you haven't changed the hit probability any). And then re-work the monsters you want to weaken under the new more granular system (after all, as DM, you can pick where the stat is, so that cat can have a Str of 2 (as he didn't roll) giving a -49 to damage on his, what, 1d3*10? EVERY hit by that cat would be falling under the 1 point minimum damage rule (which we don't change), and a peasant could laugh at the cat for half the day... well... for quite a few attacks, anyway.