How to restructure GPX / GPS track

Open a track in GPS Track Editor (File | Open track...)
If you do not want to completely rebuild the track structure, proceed to item 6 below.
Choose Track | Restructure... key.
Drag the sliders to choose the desired time gap between track segments or folders.
Click OK.
Delete unnecessary segments or folders. In the Tracks list, select an item and press Del.
To split a segment, right-click a track point on the map or in the Points list and choose Restructuring | Add break.
To join some sequential segments, select them in the Tracks list, right-click, and choose Restructuring | Join.

In the Restructure Track dialog, moving slider to the left will produce more segments / folders.