Help!! Cannot change flat tire

OK, I know that last section can be a little tricky, but I use a little lube when I do it, in a race or on the road a little scoosh from your water bottle on the section and it should help the tyre lever work round a little easier, then use a handy rag (typically your shirt I guess) to wipe off the excess and ride away, when you have time you can actually purchase tyre lube for this very reason, but something that gives the tyre lever and tyre less friction like soapy water or a little washing up liquid is ideal, again make sure it's dry and wiped off before going screaming into that tight bend or you'd wish you'd kept the flat and walked back!!

hope that helps.

I do make it a habit not to use a lever on the install, only because if you do puncture or pinch the tube you are doing everything x2, and not have any more spares. I only carry one tube and 2 co2 so I have to be careful. Next time put a little spit on the inside lip of the last six inches, this will help. Its not easy but it should not kill you either, keep practicing until you feel comfortable, getting a flat during a race should not seem like a big deal.

I use a lever to guide the last bit of tire over the rim.  I assume this is not what you're doing, since it doesn't require pulling.  I think this is what others are suggesting, since it does put the tube at risk. 

1. NUMBER ONE:  Unless you're still struggle to keep the tube inside the tire, make sure the tube is deflated.
2. Use your hands until you can't pull anymore over
3. Very carefully wedge the lever between tire and rim.  Check that the tube's not stuck inbetween.
4. Holding the opposite side in place, pull the lever along to help the tire into the rim

I have have a ton of experience, but I can usually change a used tire.  I have struggled with new tires and will usually give up, only because it's not really a race-day type of worry for me. 

It helps to have a little faith.   Get a good grip and pull it over!  It's possible, but it usually hurts a little more than you think it should

When I got new tires for my bike I just could not get them back on the rim, and I'm a reasonably strong guy. After doing some searching on the net I found a recommendation on Sheldon Brown's site for The Bike Tool (http://thebiketool.com/). I ordered it and it really does work. It takes a time or two to get used to how it works but it does work.

The funny thing is that after doing a several changes my tires have become easier to work with and I can put them back on without the tool. I still carry it with me on the bike, though, just in case.