Go to your dashboard
Once yourself and the client have agreed on the change, head to your dashboard.
You will be able to view all proposals under Latest Proposals.
There will be a list of all current proposals, click edit proposal on the one you want to edit.
Make any changes that you and the client have agreed on. This might be a change to the proposed cost, length of project or the client may want to add milestones.
Update the proposal
Update the proposal. This will be resent to the client for them to accept. Once they have accepted the resubmitted proposal, you are good to go!