byte to decimal conversion

Hello, 

I'm having a problem to read data in a binary format from a an instrument. according to the manual  The instrument send data as a word - a two byte format - in the following order:

The MSB is sent first. The LSB is sent last. EOI is sent with the LSB. 

I read it as a string and can convert it to bytes array.

how do I turn it into a real number?

thanks