If by bigger you mean zoom in on timeline contents, then with the mouse in the timeline timecode region, it changes to double horizontal arrow, left mouse click and drag left to shrink timeline or to the right to expand timeline timescale.
If by bigger you mean a video track that is larger vertically, right mouse click in a unused region of a video track and use the "Adjust Video Track Height" option.
If by bigger you mean more screen space for the timeline region, then in the middle of the screen under the media library are 5 little dots, place the mouse there, it will change to a double vertical arrow, left mouse click and drag up to shrink size of media library space and create more screen space for the timeline.
Jeff