We are talking about personal details about an individual. Think about what you store, where you store it and what you do with it.
Thinking about how you have answered the questions above, you should only be holding/storing personal information if you have a genuine reason to keep it. When the individual gave you their information, how did they think it would be used?
You should only be using the information for the reason it was collected in the first place and the individual needs to know why. It needs to be accurate and not kept longer than necessary. It must be stored securely, to avoid accidental loss or misuse of the data.
If you don’t have a ‘good’ reason for keeping the information, then you should delete/shred it.
As you read through these GDPR guidelines, it should become clear ‘what is a ‘good’ reason for keeping the information’.