How can I reduce padding after figure?

You can modify the following lengths, which affect all floats.;

• \floatsep: space left between floats (12.0pt plus 2.0pt minus 2.0pt).
• \textfloatsep: space between last top float or first bottom float and the text (20.0pt plus 2.0pt minus 4.0pt).
• \intextsep : space left on top and bottom of an in-text float (12.0pt plus 2.0pt minus 2.0pt).
• \dbltextfloatsep is \textfloatsep for 2 column output (20.0pt plus 2.0pt minus 4.0pt).
• \dblfloatsep is \floatsep for 2 column output (12.0pt plus 2.0pt minus 2.0pt).
• \abovecaptionskip: space above caption (10.0pt).
• \belowcaptionskip: space below caption (0.0pt).

Source

You could change \belowcaptionskip, for example:

\setlength{\belowcaptionskip}{-10pt}

For further customizations I recommend using the caption package. It provides a lot of features and is very well documented. If you're using the caption package, you can set the spacing as:

\captionsetup{belowskip=0pt}