If you want to move the log to g:/bigdisk/tourslog, move the log with operating system commands:
move h:\janets\tourslog\log\*.* g:\bigdisk\tourslog\log
Then, alter the logDevice entry in service.properties to read as follows:
If you later want to move the log back to its default location (in this case, d:\mydatabases\toursDB\log), move the log manually as follows:
move g:\bigdisk\tourslog\log\*.* d:\mydatabases\toursDB\log
Then, delete the logDevice entry from service.properties.