Later versions of FL Studio, 12 and higher, feature a vector based Graphic User Interface (GUI) that automatically adapts to your screen resolution as set under 'Windows Control Panel > All Control Panel Items > Display'.
Plugins are hosted inside FL Studio and may show up very large, while others appear too small. There are solutions to these problems outlined in the user manual under:
'General Settings > GUI Scaling' and 'Wrapper Settings > Rescaling VST plugins'
Image-Line Support Team