You are about to upgrade from a previous version to DAM for Sitecore (DFS). Which requires yours attention.

Before updating to 9.1.0:

If you are upgrading from DFS 8.x follow this step, otherwise continue to the next step.
We have removed the member- and role providers in this release. Which means that you have to remove them from Sitecore's web.config.
1. Navigate to the <membership section and remove the node with the name DefaultDigizuiteMembershipProvider.
2. In the same section, find the node with the name Sitecore and change the realProviderName to sql.
3. Navigate to the <roleManager section and remove the node with the name DefaultDigizuiteRoleProvider.
4. In the same section, find the node with the name Sitecore and change the realProviderName to sql.
Before installing DFS 9.1.0, it is very important that your silo item is backed up. The silo is located at sitecore → Media Library → Digizuite. The installation will remove this item, and all content pages will have broken links until you revert the silo item back to your solution. It is very important that the silo ItemId is the same before and after the installation.
1. We recommend using the Package Designer to backup the silo item.
2. Delete the silo with "Leave links" option
3. Confirm items under Digizuite have disappeared:
4. Empty data in dfs_assets_master_index and dfs_assets_web_index. Ensure solr core replication does not interfere with this (if any).

Updating the module to DFS 9.1.0

After updating to DFS 9.1.0:

If you are upgrading from DFS 8.x, follow this step otherwise continue to the next step. Since we removed the DFS membership provider. You have to assign the role sitecore\Digizuite DAM for Sitecore Users to the user extranet\Anonymous. If you don't do this, you won't be able to see any DFS assets on the public website as the anonymous user.
Add the silo item through the Installation Wizard again which you packed in step 2a.

It is important to delete the data of the index dfs_assets_master_index, before doing a full synchronization of the silo. If you dont do this, the full synchronization will fail.
After having done the above, continue with step 3 of the installation guide: DFS 9.1.0 - 3 Setting up Sitecore