If you're importing large numbers of Contacts and they've got multiple membership types, then consider splitting up your imports and import them directly into Groups.
This will allow you to easily move large numbers of Contacts into your new TidyHQ Membership Levels.
To do this, you should sort your CSV by the column that includes the membership name you're using.
Below is an example of what your file may look like (using Excel) but you may have different fields and field names or be using a different spreadsheet app.
Using the above data as an example, you could cut & paste this information to create a new CSV file and then import the data into a Group:
Importing your Contacts into Groups will make it a lot easier to import them into the right Membership Levels.