They are quite simple to change. However why did you buy new ones? They typically last many more years than the age of your Summit. My Summit from early 2000's (forgot exact year I bought it) still has original main burners. I only needed to replace the crossover tube burners. Otherwise the burners are maybe 16 years old. I replaced the crossover tubes in 2009 or 2010. The flavorizer bars are original also FWIW.
When you say bottom rusted out do you mean the cabinet or the fire box? Truly the fire box is the weak link on Summits