In DNN we can apply Skin in three ways

1) Host Level - In Host > Skin

2) Admin > Skin

3) Tab Settings

First find out which skin is appled for home page tab

Once you found applied skin

Search  in sking ascx file

<dnn:USER runat="server" id="dnnUSER"  CssClass="user" />  &nbsp;&nbsp;|&nbsp;&nbsp;<dnn:LOGIN runat="server" id="dnnLOGIN"  CssClass="user" />

find appled CssClass, here user is class will find in skin.css

.user,a.user:link,a.user:active,a.user:visited { color:#3E81B5;font-size:20px;font-weight:bold;}
a.user:hover{color:#C00;}

and add your desired font size and font weight

Regards

http://www.leosys.net