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You can adjust the seat height by pulling the adjustment lever upward.
Literal
Adjustment-lever [object-を] upward raise [when-と] seat-surface [genitive-の] height [object-を] can-adjust.
Product-manual instruction style. Two structural points: (1) The ~と here is again the 'automatic consequence' conditional — pull up the lever, and the adjustment becomes possible as a natural result. (2) 調節できます is the polite potential of 調節する — 'can adjust.' Note the slight redundancy in 上に上げる ('raise upward') where 上げる already means 'raise/lift up' — but Japanese often adds 上に for directional clarity, especially in instructional contexts. 座面 ('seat surface') is the flat part you sit on, a technical term in furniture and ergonomic contexts.