Yes, you can upgrade/downgrade your services at any time.
Login to your client area and then select Services > My Services, pick the service you want to upgrade/downgrade then click Upgrade/Downgrade from the options menu on the left.
From there you can select the plan you wish to upgrade/downgrade to.
If you do not have the option to upgrade/downgrade please submit a support ticket here and we can look into this for you https://mwnetworks.online/clientarea/submitticket.php