How to Change the Number of Recent Items Shown on a Mac

Part 1 of 2:

Click the Apple menu. You'll find this in the upper-left corner of the screen, regardless of which program is open.
Click "System Preferences."
Click the "General" option. You'll find this in the upper-left corner of the System Preferences menu. If you don't see the main System Preferences menu, click the "Show All" button at the top of the window. The "Show All" button has 12 dots arranged in a grid pattern as an icon.
Click the "Recent Items" menu.
Click the number of recent items you want to display.^[1]

Part 2 of 2:

Click the Apple menu.
Highlight "Recent Items."
View the items in the list. Note that the list will still show the previous number of items at first if you increased the size. For example, if you went from 5 items to 15, the list will still show 5 items in each category until you start opening more apps and files.
Click "Clear Menu" to empty the list. This will clear the list out, and it will start building up again to the limit you set.