If you mean you entered your new weight on your weight graph in My P.L.A.N., and your weight didn't change on the graph, did you remember to scroll all the way down to the bottom of the page and click on Save Changes? Even then, the new weight sometimes doesn't show unless you click the Refresh button on your browser.

The weights shown to the right of your posts are not related to the weights you enter in My P.L.A.N. To adjust them, you have to go to your User Control Panel and click on Edit Profile. (You can get to your Control Panel by clicking on User CP on the far left of the green tool bar, or by selecting Edit Profile under the Quick Links function on that tool bar.) Make the necessary adjustments to your weight there, scroll all the way down to the bottom of the page, click Save Changes, and you're done.