Your mobile phone number and personal password are used to access your Cloud account. Therefore, a change of your mobile plan will not have any impact on the access to your storage. Only if you change your Orange phone number yoiu will have to migrate your Cloud data from the your former phone number's account to the new one.
Use the application menu if you wish to upgrade or downgrade your Orange Cloud plan.
If you want to delete your datas, just uninstall the Orange Cloud application. You may download the content of your cloud account to another personal storage and delete your data from your cloud account at any time you want.
If you terminate your subscription, you will be given a 2 month time limit to get your data back on another support. You will still be able to connect to the service using the same IDs but you won't be able to add new files to your Cloud account.