Hopefully that fullname calculation is First name & Second Name--not First Name + Second Name.
It'd be much better design to link by a serial ID field. Names are not unique and subject to change--just to name two potential problems.
Neither of those details affect the issue at hand, however.
You have two methods you could use to access the most recent membership record:
You can use the Last () function to refer to related data in a calculation and it would reference the last related record instead of the first.
You can also go into Manage | Database | Relationships, find the relationship line linking your two tables (table occurrences actually) and double click it to bring up the details on the relationship. There's a sort option you can choose to sort the records in descending order--assuming you have either a date field or serial number field in membership that you can sort on to get this order.