Log in go to help then open a chat. Tell them your old number is disconnected by the network and you want to link and confirm a new number. Someone will phone you on your new number and link it and confirm with a PIN. Be careful some agents really hate their jobs and will waste your time.
You forgot to clarify to add a new number, support will give you many questions, address name, date of birth and others,
for US paypal you will be asked for SSN, and may ask for credit history or backgrounf report, it all depends on the person in paypal support
PayPal login 
