It will be cheaper and easier to buy a different truck.
But, if you're determined to throw your money away, you'll need a transfer case, front driveshaft, rear driveshaft, front axle, front half-shafts, transfer case shift motor, dash switch, transmission tail shaft housing, and possibly a new transmission, transmission control module, and possibly some revamping of related systems (ecu, abs, etc.). That last part isn't likely but it is possible.
When you gather the parts cost you'll see you could sell your 2wd, and buy a newer 4wd, for significantly less. My off the cuff guess is parts will run you 3-4k, conservatively, and maybe more than double that if a new trans is required, rather than just a new tail shaft housing.
I figured thanks for your honesty I have another quick question what type of grill guard do you recommend for my model if you know any websites or galleries that could give me a better insight and thank you