Release notes and a migration guide for your frontend code are available at
https://sdk.dfinity.org/docs/release-notes/0.8.0-rn.html
You can install the latest version of dfx with
sh -ci "$(curl -fsSL https://sdk.dfinity.org/install.sh)"
And I have a writeup on the frontend changes on my blog at (note: 0.8.0 is largely the same as 0.7.7, it is just the official version we have added to the manifest).