SPTrade is what is used to exchange in your character's stat, skill and advantage points The command should be available to you any time outside of character generation. The cost of increase for a particular stat or skill will be displayed in ()'s beside the stat or skill. All you have to do is type the number of the item you want to raise. It is a good idea to raise stats that correspond to the skills your character has, making those skills more effective. (See 'help skills' for a list of what stats go with which skills).
You may exchange AP for Advantages using this, though some advantages have pre-requisites and requests will be reviewed to see if your character meets any additional IC / RP requirements.