Upper GI haemorrhage with dyspepsia and weight loss- How to investigate further?

Male, 82 years old, with personal history of Hypertension, Dyslipidemia and Aortic valvuloplasty. He was admitted in our hospital for several presyncopal episodes. In the anamnesis was remarkable a several-months history of dyspepsia, weight loss of more than 10 kg and melena. What can be the differential diagnosis of his clinical presentation and how to investigate it further?