I have a 2003 Ford Focus and its not shifting properly?

[Justwondering]

I don't know anything about cars and therefore don't like mechanics they usually take advantage of me lol. My Focus used to shift great and then one day started not shifting right it has trouble shifting in 1st and 2nd and don't shift into third and slams into fourth gear. My friend put it on a diagnostic and he said that it gave a solenoid code and a bad ratio code but he stated that a bad solenoid could be giving it a bad ratio im hoping its not the whole trans and is just a solenoid or something so anyone that might know please help