You can easily take a package off sale by going to Packages > click on relevant package > Remove from sale.
When you take a package off sale, the package returns to "draft" status. Clients will no longer be able to buy it.
Clients that have already bought the package will not be affected. They will still be able to use their packages.
Please note that if you remove a pass that has auto-renew enabled on it from sale, any purchased instances of it where auto-renew has been turned on by the customer will not auto-renew due to the pass no longer being on sale.