How can i make my dirtbike bigger?

Im not talking about speed wise..i want my dirtbike to be the size of a 125 or 250...im about 5'8 and 120 lbs and i have alot of experience in dirtbikes...ive been rideing for around 6 years..i want a 125 bad, but we cant afford that rite now..the bike i currentlly have is a kx 100. i dont exactly remember the model but i think its around an 01 or and 02. It has been raced several times..but im currently just crusing around with it.. but its way to small for me. i need to know how i can make it the size of a 125 or 250 to make it fit me better. :) ty