Summarize the following:
If you don't have IDM yet, download it from https://www.internetdownloadmanager.com and install it before continuing. This is a gear-shaped icon at the top of the IDM window. It's on the right side of the Internet Download Manager Configuration page. Click the drop-down box {"smallUrl":"https:\/\/www.wikihow.com\/images\/1\/1e\/Android7expandmore.png","bigUrl":"\/images\/thumb\/1\/1e\/Android7expandmore.png\/30px-Android7expandmore.png","smallWidth":460,"smallHeight":460,"bigWidth":"30","bigHeight":"30","licensing":"<div class=\"mw-parser-output\"><p>I edited this screenshot of an Android icon.\n<\/p><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"http:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a><br>\n<\/p><\/div>"} below the "Connection Type/Speed" heading near the top of the page, then click the High speed option. The high speed option is entitled High speed: Direct connection (Ethernet/Cable) / Wi-Fi / Mobile 4G / other. Click the drop-down box {"smallUrl":"https:\/\/www.wikihow.com\/images\/1\/1e\/Android7expandmore.png","bigUrl":"\/images\/thumb\/1\/1e\/Android7expandmore.png\/30px-Android7expandmore.png","smallWidth":460,"smallHeight":460,"bigWidth":"30","bigHeight":"30","licensing":"<div class=\"mw-parser-output\"><p>I edited this screenshot of an Android icon.\n<\/p><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"http:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a><br>\n<\/p><\/div>"} to the right of the "Default max. conn. number" item, then click 16, 24, or 32.  Only perform this step if your computer, router, and connection type are all high-performance models. Otherwise, increasing connections will actually decrease download speed. Using the maximum number of connections available may get your IP address blacklisted on some download sites if you download more than one file at a time. It's at the bottom of the window. This will save your connection settings.

Summary:
Open Internet Download Manager. Click Options. Click the Connection tab. Change the connection type and speed. Change the number of connections. Click OK.