All your Football Manager game files can be found in the following location by default:
C:\Users\[Your Windows Username]\Documents\Sports Interactive\Football Manager 2018\
We very much suggest having auto save turned on to weekly or fortnightly with ‘New File for Each Auto Save’ so you always have a recent backup of your save. If you find you have a large number of backup saves, you can manually delete them from the location show above.
You can change you auto-save settings via the in-game preferences at any point. Bear in mind auto save will save at the time period set by the user from the last time you saved. If you manually save at any point, the auto save clock restarts.