The process of exporting, trimming and then importing back may likely result in too many items that are not in balance or incomplete. It may require significant time and effort to find and correct any discrepancies. Cropping prior year transactions will give incorrect balances going forward.
QuickBooks has a utility to condense the file that will reduce the file size that is certainly more reliable; but it may or may not be enough of a change in file size if you keep seven years of detailed transactions. See http://dataservices.intuit.com/support/pages/inproducthelp/core/qb2k12/contentpackage/core/file_condense/info_condense_data_file.html for Intuit support information and links on the procedure.
See also http://support.quickbooks.intuit.com/support/articles/HOW12161
"The Condense Data utility stream lines your company data file by condensing
closed transactions into summary journal entries and removing unused list
elements. The utility creates a journal entry for each month in the selected
period. The summary journal entries affect your accounts in exactly the same way
as did the detail transactions.
The following section lists some important functions to consider before
running the Condense Data Utility."
Those considerations need to be reviewed prior to using the tool to condense.
Also, it is possible to create a new company file for each new year, by performing the Clean Up Company Data or Archive & Condense Data procedure as explained at http://support.quickbooks.intuit.com/support/articles/INF12329
"Your new company file retains your lists, preferences, and service
subscriptions, but no transactions. You may begin entering opening balances for
Balance Sheet accounts by selecting Make General Journal Entries from the
QuickBooks Company menu."
This can be used to prevent the file from continually expanding each year in the future.
The utilities will be more efficient that using Excel for cropping prior transactions.
Please ask if you need clarification or discussion.