Solving memory issue on ec2 instance

I created an fresh ec2 instance, following this post.
After successful installation and working of lecture notebooks.I started downloading a different dataset from kaggle of 5 gb. But soon it started giving low memory errors.

On running df -h:

we can see 100% usage of directory /

Again watching what really consumes the space on fresh installation :

I want to ask which directory can we safely delete so as to increase the space.