There is a plugin (described in Hansmex' plugin guide) that allows various advanced editing features - resizing being one. The plugin is very useful, but be careful to save your work as the results sometimes can be a bit strange.

IF you have several levels, you may also want to try the latest beta of SH3D where you can select across levels. Just tried resizing a multiple level design to 107,5% and it worked like a charm....

ok