The first step in calculating the required sample size or to see if you have enough power to run your experiment is to open R.

The first time you use R for this, you will need to type:
and hit 'Enter' on the keyboard. This will install the R library that you need to carry out the power analysis. This library was developed by Stéphane Champely, and calculates power based on Cohen's (1988) protocols.
Next, type:
into the console and hit 'Enter'. You will need to do this every time you open R to carry out a power analysis. This will make the 'pwr' library active (you always need to do this in R when using a library during a session, so get used to doing it now!!).