You can easily update properties in Hubspot to reflect any changed information you know about contacts eg phone number. You can also add new information that you discover through your conversations with them.
To do this, hover over the property you want to update and hit the pencil icon.
You can also create notes against your contacts to record additional information you need to remember. To do this, you simply hit Note in the left column, type your details and save. It will then appear in the activity section (the middle column in Hubspot.)