docs: Update upgrades doc

Add notes on deleting assets and major version updates.

docs/technical_documentation/how-tos/upgrade.rst

@@ -8,8 +8,15 @@ At least in the early phases of existence, Aspects is intended to have a faster
 As for any upgrade you should take a backup snapshot of your environment before beginning, especially make sure you have a recent backup of your ClickHouse database. Then follow these steps, which are basically the same as installation:
 
 - Install the version you would like from tutor-contrib-aspects, or for the latest: ``pip install --upgrade tutor-contrib-aspects``
+- To prevent orphan Superset assets from being left behind, you should remove the existing Superset assets from your Tutor environment before saving the configuration: ``rm -rf env/plugins/aspects/build/aspects-superset/openedx-assets/assets``
 - Save your tutor configuration: ``tutor config save``
-- Build your openedx image (in case there are upgrades to LMS/Studio plugins): ``tutor images build openedx --no-cache``
+- Build your Docker images: ``tutor images build openedx aspects aspects-superset --no-cache``
 - Initialize Aspects to get the latest schema and reports, for a tutor local install: ``tutor local do init -l aspects``
 
 In a case where the release has special instructions, such as when new xAPI transforms have been added and you may need to replay tracking logs, they will be included in the release announcement.
+
+
+Major Version Upgrades
+----------------------
+
+When upgrading between major versions of Aspects, such as from 1.x to 2.x, take special note that there *will* be breaking changes and there may be new limitations on compatibility with older versions of Open edX. For instance Aspects version 1 was designed to work with Open edX named releases Nutmeg through Redwood, while Aspects version 2 is designed to work with Redwood and later. If you are upgrading from Aspects 1.x to 2.x, you must have compatible versions of Tutor and Open edX installed.