You can't. The i5 4200U is on a BGA socket meaning it's soldered to the MB. You can only change it if you take it into an IT service that has a rework machine, but it is an expensive procedure, and more of a fuss.
Can you? Maybe. You'll have to check to see exactly what CPU's are supported. But since you already have an i5, you probably won't see a lot of difference with a different one.
You can't. The i5 4200U is on a BGA socket meaning it's soldered to the MB. You can only change it if you take it into an IT service that has a rework machine, but it is an expensive procedure, and more of a fuss.