Library : A well defined set of instructions which provide unique properties and behavior to your data.
Framework : A collection of libraries which provide unique properties and behavior to your application.
When you have a library you need to understand the functionality of each method and it is relatively hard to create complex interactions.Frameworks, on the other hand, contain the basic flow and since you only need to plug in your behaviour.
If you don't like the jQuery date picker library, you can replace it with another date picker such as bootstrap date picker.
If you don't like Angular on which you built your software, you can not replace it with any other framework. You need to rewrite your entire code base.