Set Size

Dimension dim = new Dimension(300,200);
jLabel1.setPreferredSize(dim);
jLabel1.setMinimumSize(dim);
jLabel1.getParent().revalidate();

Reset:
    jLabel1.setPreferredSize(null);
    jLabel1.setMinimumSize(null);
    jLabel1.getParent().revalidate();

Note:
    The specifics of which "size" method to use depends on the layout of the Parent

Set Font

jLabel1.setFont(new Font("Courier New", Font.BOLD | Font.ITALIC, 23));

Reset:
    jLabel1.setFont(null);

Set Foreground Color

jLabel1.setForeground(Color.GREEN);

Reset:
    jLabel1.setForeground(null);

Set Background Color

jLabel1.setOpaque(true);
jLabel1.setBackground(Color.RED);

Reset:
    jLabel1.setBackground(null);

Set Border

jLabel1.setBorder(new LineBorder(Color.MAGENTA, 4));

Reset:
    jLabel1.setBorder(null);

Set Text and Icon Gap

jLabel1.setIconTextGap(40);

Reset:
    jLabel1.setIconTextGap(4);