Main Question or Discussion Point
Im designing a PCB and i need a software that is able to change the size of the components (e.g. the length of the resistor).
It that really free? What's the catch? Can you sent the gerber to any place? Sounds like you need to go to particular place to fab the pcb.What do you mean by "change the size"? Resistors and other discrete components only come in a limited range of sizes. If you are using the correct libraries for the tool, all the standard sizes should be available to you. Note that for discrete components, not all values are available at all sizes.
Regarding software, I've found PCB123 to be reasonably good software for the hobbyist on a budget.