There's a thread here that explains all about the weight tracker. This is the bit you need I think.
Quote:
2. Edit your signature tracker code. You can keep the same images without having to make a new code, and just update your weight.
* Look at your code and you will see three numbers that represent your Starting weight, Goal weight, and Current weight. The last number is your current weight and is the only one you need to change.
* Change the current weight to your NEW current weight. Make sure you don't change anything else, or you may have to go make a new tracker. Now save your signature.