You can install LispWorks 7.0 in the same directory as previous versions such as LispWorks 6.1. This is because most of the 7.0 files are stored in a subdirectory called lib/7-0-0-0.
Binaries produced by cl:compile-file in previous versions of LispWorks do not load into a LispWorks 7.0 image. You must recompile all your code with the LispWorks 7.0 compiler.
LispWorks Release Notes and Installation Guide - 2 Mar 2015