You can buy pickups or sets of pickups. Good ones can be expensive, but manufacturers sell online, plus there's eBay, and there are lots of recommendations online, too. The trick is to have pickups which complement each other - manufacturers will often advise on this - and are a good match to the wood/type of guitar. The work itself doesn't have to be difficult. If you have pickups which fit the pockets in the body, there's little more to do than a bit of wiring.
I don't have experience of this, but I looked into it for possible new pickups on my Yamaha, and the guitar kit I was thinking about last year.
I don't have experience of this, but I looked into it for possible new pickups on my Yamaha, and the guitar kit I was thinking about last year.