well in 7.3 it has many modules added, fixes.
There's no problem in upgrading from 7.1 to 7.3
Because all you have to do is to upgrade your database.
All table structures are the same. However there are some added table just like in CASH RECEIPTS ENTRY, currently on CASH RECEIPTS ENTRY the affected tables for the entries here are ARINPPYT, and ARINPPDT. But now it added ARINPSTLHDR. This is for the settlement entry. Because in 7.3 there is no SETTLEMENT ENTRY which has full of problems.