Look at the bottom-right corner or the Settings menu. Ensure the "Speed Limit" checkbox is unchecked. If it is checked, the software will cap your speed at whatever value is entered in the box—often a default of 10 KB/s.
It’s common to accidentally toggle a limit or for the software to default to a restricted state. how to increase download speed in jdownloader 2
This splits a single file into multiple parts that download at once. A setting of 2–10 is usually ideal. Setting this to 20 or higher is rarely helpful and may get your IP temporarily banned by some servers. Look at the bottom-right corner or the Settings menu