OK. If you are Alliance and you want to get your first aid over 150, you need to travel to Stormgarde Keep in the Arathi Highlands. Of the 3 NPCs you can see for this, the one in Stormgarde is the easiest and safest to get to.
Deneb Walker is the man you want to see and he is located on the Alliance side, in the garden area, on the right side as you cross over the bridge. He is not a trainer. He is a vendor of scrolls and potions. He will sell you the book for a mere 90 silver. Once you have the book simply right click it and it will boost your maximum skill to 225. You will NOT get any new recipes, you will not pass go, and you will not collect 200 gold.
If you are unfamiliar with Stormgarde Keep, simply run into the castle and at the crossroads, turn right and head west to the alliance side. Follow the path to the right always going right as the path leads you and across the bridge. You will see a vine covered structure in front of you and immediately to the right of that structure you will find Deneb.
Hope this helps. Be safe and have fun.