volume delete

we have 2 vnx 5400 and 2 vplex . some preconfigurations have been made but I have no complete knowledge.  Areas with 1 and  5 TB are not used.

1- but not sure so I want to find out if they use them?

2- how can I delete them?

3 - I want to give back to vnx 5400 storage so I will include it in the pool at vnx 5400

4-  Please write the steps. thanks for helping