To downgrade your W3dart account to a different plan, you need to do the following
1) Login to your account https://app.w3dart.com using your email and password.
2) Go to Account page : https://app.w3dart.com/account/overview
3) Click on Plan tab : https://app.w3dart.com/Account/my_plan
4) Select the desired plan you want to downgrade.
Note : Make sure you have allow number of Live and Archived projects allowed in the plan you wish to downgrade.
If you have more then allowed project you will be promted to make the changes to the project list.