The following links will take you directly to the installation page in Salesforce:
Important! Make sure to always install “For Admins Only”.
Install Subscription25 v1.304 in a Sandbox
Install Subscription25 v1.304 in Production
If you install this for the first time you should follow this step https://gen25-jira.atlassian.net/wiki/spaces/SUB/pages/2624356356.
On a production environment you might need to add the correct permissions first. The needed steps are documented here: https://gen25-jira.atlassian.net/wiki/spaces/SUB/pages/354779149