In the $HOME/.config folder there are files created by many different programs, and as such there is no easy way to manage them all.
These files should be created/managed/removed by each single application, and deleting them can (will) result in loss of data (personal configurations in this case).
Being that all the data contained should be configuration data, this folder should not contain a lot of data, 300MB is quite a lot of config.
You can enquire which subfolder contains most of the data by using the command:
du -sh ~/.config/*
and you can see by yourself which folder has grown out of control.