I am not support staff, just a user.
As far as I know there is no way to make bulk changes to either of the things you want to change unless you can write python scripts, even then I can’t confirm it can be done.
The quickest was to remove securities from the list of securities on the Summary page in the stock price section is to click on each security you don’t want to appear, then EDIT and untick its “Show on Summary” page box.
However, if these are the same securities you want to change from "Avg. Cost" to "Lot Matching" then selecting each security in the security detail window and the then using the HISTORY – EDIT button then untick its “Show on Summary” page box and then EDIT SECURITY button for "Avg. Cost" to "Lot Matching" is probably quicker.