Just like an AR15. Remove handguard/gas tube, remove barrel nut, slide barrel out of upper receiver - reassemble in reverse.
**Note** Some handguards attach via a proprietary barrel nut that sometimes requires a proprietary barrel nut wrench.
I did a barrel swap on a DPMS LR308 quite a few years ago and have receiver vice blocks. I also have a Daniel Defense large frame barrel nut wrench. I'm about 45 minutes north of the metro if you'd like to use them.