expression, ichidan verb
examine tickets; check tickets
Used for the act of inspecting or validating tickets, typically by a conductor or staff member.
車掌が乗客の切符を改める。
The conductor examines the passengers' tickets.
改札 refers to the ticket gate or the act of checking tickets at a gate, while 切符を改める is the specific action of examining a ticket.
Compound of 切符 (ticket) + を (object marker) + 改める (to examine, to check).