"pick you up" is the only correct one of the two you listed. Getting into more details though, note that this is a pattern involving a verb and an adverb, which has a dual form. 1. I'll pick you up - [Verb + PRONOUN + Adverb] if the object is a pronoun. 2. I'll pick up my friend - [Verb + Adverb + NOUN] if the object is a regular noun (phrase). So we say "I botched it up" and never "I botched up it", for example. But also note that there are similar looking phrases with a preposition, for which we must put it before the noun or pronoun. For example, - I rely on you - "on" here is a preposition, so it cannot come after "you". "up" and "on" can be both an adverb and a preposition, so it is not always obvious which capacity they are being used in. You need to have a good understanding of their general usages, as well as how they combine with certain verbs. For example, here are more complex cases. - He took off his jacket - is "off" an adverb or a preposition? - He took his jacket off - "off" is an adverb, so it can come before or after a noun. - He took it off - but not before a pronoun. (We know "off" is an adverb because it describes the whole action ("separating"), not limited to the "jacket") - I'm going to beat him up - adverb. ("up" describes thoroughness of the action) - I walked up the grade - preposition. ("up" describes how the action relates to the grade primarily) - The children look up to their teacher - "up" is an adverb, "to" preposition (some people consider "up to" as a compound preposition).

You can also say "I'm going to pick up someone from somewhere." Examples: " I'm going to pick up my friend from the airport. " "I'm going to pick up my cousin from the bus station. "He's going to pick up the kids from school today. "

I'm going to pick you up. Phrasal verb: pick (somebody) up