the guys I like are skinner than me and kinda band dudes! and never go for me so I'm changing my body to 3 or 2 sizes smaller than I am now and changing my hair and getting a new kick ass load of clothes,but this means I'm changing who I look like is it really worth it ? like realistically am I going to be in with more of a chance now?
If you're making all those changes because it's what you want, it's worth it. But if you're just doing it to impress other people, it's not.
You might have a better chance with those guys, but only if that's who you really are. Guys generally like girls who are comfortable being themselves, so if a guy is interested in you, he'll accept you as you are.
You should only make changes for yourself, not for the sake of others. An important question you should ask yourself is will this guys change for you?
Probably not, because people don't change for others, they change for themselves. I assume you want to change for your own purposes as well. If this change does not interest you for your own self image/worth then you really need to stop and ask yourself what it is you're doing.
I think that changing things about yourself for the better is a good and healthy thing as long as it is for YOURSELF and not other people. People are going to like or dislike you regardless of what you look like. But if you are doing these things to boost your confidence, I say go for it. But always be true to yourself and never doubt what you have to offer beneath your appearance :)