No, just fix the weight now.
If you want to weigh in kgs you can do that, but you have to set the system to say you're using kgs. You will get a 'blip' in charts as it just charts the raw value, but your calories burned will be right again.
On the My Goals section click the 'change' link for Weight and set there your kg amounts for start and goal and that you want to use kg's.
Then go to Account/Email Preferences and check the box for Use Metric.
You should then be using kgs.
Deb, in New Zealand