According to Westside literature available, beginners should switch every 3 weeks and advanced lifters every week. Advanced lifters often have more variations they choose from.
Beginners typically choose variations closer to the main lifts and fewer variations. As one's training age increases, exercises further away from the comp lift are needed to work specific weak points and give the body a different enough stressor so the lifter doesn't burn out. At least according to Westside principles.
If you lift raw, you'll probably need some more dedicated quad work than you typically see in most westside splits. You'll also most likely want to let your knees drift forward some and not like a Westside style box squat. You'll also want to use about +/-10% more of your max for the DE lifts.
To many people, the lack of practice of the main lifts is an issue with Westside and I'm inclined to agree. So I set up basically a Westside split that's whole body 3x/week and rotate each lift through DE, RE, ME methods. For me, it keeps things interesting while still practicing each comp lift every week in one of the methods above. It also makes me more selective about the exercises I choose because I only have so much in me after doing some kind of deadlift/squat and bench type movement.
If your new into Westside, I highly recommend Jim Wendler's Max Effort book. I think its the most well written piece of Westside literature there is. Also, look up the squat manual by David Tate on elitefts. Dave tate's bench manual is very good too.