1. Do you have a static IP and is it going to change? If so then you'll need to go into the local management of the MX and change it there (navigate to http://mx.meraki.com/ in a browser)
2. If you have already set traffic shaping, you'll probably have to change it as the SDSL should have a higher upload and possibly download too, in the Meraki portal go to Security appliance --> Configure --> Traffic Shaping
Not sure about the ramifications of any changes in PPPoE but the provider should be able to help you out with that.
Also, if you have any external DNS pointing to your existing IP and it's going to change, you'll have to update the existing DNS.
I'm sure others will chime in with more stuff but that's what I can think up.