I'll be flying Delta for business in a couple weeks, round trip from LA to Tampa. I've never flown Delta, unless I did as a child and don't remember. I'm hoping some of the Delta regulars can give me some tips... I'm booked for standard economy aisle seats for both flights. Is it possible to get upgrades to either first class or comfort plus? How common is it for upgrades to be available? How much do these typically cost? Should I check online a day or two before my flight? Or should I try at the gate? I assume Delta has a program similar to SWA rapid rewards....do I need to join this to be able to purchase an upgrade? Thanks for any advice!