You can't, unless you have booked storage capacity in Cushing, Oklahoma.
The whole issue is that there is no booked storage capacity and holders of the May WTI contract for physical delivery (without booked storage capacity) are unable to roll their positions into the next contract month of June.
Most people trading futures contracts with physical delivery never actually take physical delivery. They either close their positions (net them off) or they roll them into the next calendar month's contract.
It would appear that traders have either waited too late to roll their positions, or they have tried to buy storage capacity and realised there is none available.