LTSPICE - Scale dimensions
First you need some model files for your transistors. The model files need to be included by using the .lib command. Make sure that the model file takes care of calculating the dimensions required to get the parasitic capacitances.

You need to use generic transistors (nmos4, pmos4).

The scaling is simply done by specifying the w (width) and l (length) of the transistor.

See the example below.