Are the tips on a surface cleaner (such as the BE units) hard to change? Is it just a screw off the old tip and screw on a new tip job or is it more to it than that?

Also, after doing the math it seems that the 24" BE unit will give me 2000psi with the "stock" tips..... would this be enough cleaning power for normal concrete cleaning (patios and driveways). Would it be faster and more benificital if I droped down to a 015 tip to raise the pressure up to 3000psi?