I have maxed out my farm, how do I get more free population?
This did not answer my question. I do not have any ships at the moment, but I need 5 people to add a seat to my senate and I only have 3. Do I need to kill off some of my soldiers>?A lot of people employ a strategy of strategically demolishing a bunch of buildings that are unhelpful in a city, for example in a Light Ships nuke city many players will only have a 20-25 quarry since stone is not needed as much, hence allowing them to build more LS and hit harder.
Many players keep there entire city maxed out in order to have the adaptability of quickly and efficiently changing the type of units built in the city, this comes at the cost of not having as much free population available.
In the end it comes down to how you play and what you are comfortable with, remember farms and warehouse cost zero pop and therefore should always be maxed out, and temples are the most expensive (pop wise) to build up to max so be careful on how high you upgrade it if your worried about pop cost.
Lastly, many event will give you a population expansion token you can apply to your city giving it a larger population size, these token stack and can increase a towns pop size by a maximum of 300.