You can do this without any external programs by modifying the registry. According this video on how to Make Windows 10 Taskbar Thumbnails Bigger:
- Open registry - Win + R and type
regedit
- Go to path
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Taskband
- Add new DWORD 32 Bit Value
- Key: MinThumbSizePx
- Value: Number of pixels anywhere less than 500
- Restart Explorer with any of the following methods:
- Longest - Restart Computer
- Medium - Log off and then log back on
- Shortest -
- Ctrl + Shift + Right click on Taskbar
- Select 'Exit Explorer'
- Pull up Task Manager (Ctrl + Shift + Esc)
- File > 'Run New Task' > Type
explorer
- Voila! You've restarted explorer