How do you make your upkeep lower ?

Build more farms, reduce troop count, or do research

Don't worry about upkeep, you don't lose troops if you're not paying upkeep. Once your upkeep is higher than your production then you just need to make sure you're not going over your warehouse limit for food.

Set up an alliance food bank with no/very few troops that everyone can send food trades to and keep your food items unopened in your inventory