The short video tutorial below shows how to change Trados shortcuts in Word 2007 (this version of Word is in Spanish, but the placement of the menu options is the same in English, so hopefully it will help even if your version of Word is in a different language).
I like setting the most common Trados commands to shortcut combinations that can be accessed with only my left hand, as opposed to the two-hand approach of default Trados shortcuts, so this is what I use:
Alt+Z - Open/Get (Word macro name: tw4winOpenGet.Impl)
Alt+A - Set/Close Open/Get (Word macro name: tw4winSetCloseOpenGet.Impl)
Alt+Q - Translate to Fuzzy (Word macro name: tw4winTranslateToFuzzy.Impl)
Alt+G - Get Translation (Word macro name: tw4winGetTranslation.Impl)
Alt+E - Copy Source (Word macro name: tw4winCopySource.Impl)
Alt+R - Restore Source (Word macro name: tw4winRestoreSource.Impl)
The one shortcut I have that requires two hands is for the Clean* command:
Alt+L - Clean (Word macro name: tw4winClean.Impl)
*Note that this Clean command won't update your TM.
Keep in mind that since this is a Word feature, the new shortcuts will only work in a Workbench+Word combination, not in TagEditor.