升高 is a resultative verb compound: 升 ('to rise') + 高 ('high') = 'to rise to a high level, to go up, to ascend'. You can split it with 得/不 to form potential complements: 升得高 ('can rise high'), 升不高 ('cannot rise high'). It is commonly used for physical measures (temperature, altitude, level) and for abstract things like prices, status, or volume.