That depends how big the differences between the two versions is.
htdocs files are no problem, but database files can be.
It is recommend to do a clean database dump and recreate the databases from this.
And DON'T replace the mysql, information_schema, performance_schema or phpmyadmin database with old ones.
P.S.: Due to a Bug in MySQL it is recommend to use the second latest XAMPP version not the latest.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~free software according to purpose of usageXAMPP 1.8
for local development/testing onlyZend Server 6 (free)
for production environments
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~It's like porn for programmers