Changing the font size is pretty easy. I'm gonna show you some code from the windows. The highlighted part is what you will need to change. If you want to change the font in the Target window, you'll probably want to change it in the Implied Target window as well.
Look for these lines of codes in the file eq2ui_mainhud_target.xml
<Page AbsorbsInput="false" Location="0,-1" Name="v0" ScrollExtent="370,70" Size="370,70" Visible="false">
<Text AbsorbsInput="false" actiontype="Target" DynamicData="/GameData.Target.Name" Font="
/TextStyles.Small.SmallStyle" LocalText="Ambassador Rotgaf of Freeport" Location="248,20" MaximumSize="1700,1700" MaxLines="2" Name="Name" PackSize="absolute,fixed" PackSizeProp="0253/0001,0002/0003" ScrollExtent="117,28" ShadowStyle="/ShadowStyles.Outline1" Size="117,28" TextAlignment="Center" TruncateElipsis="false">Ambassador Rotgaf of Freeport</Text>
AND:
<Page AbsorbsInput="false" Location="0,-1" Name="v1" ScrollExtent="370,70" Size="370,70">
<Image AbsorbsInput="false" BackgroundColor="#00FFFF" Location="256,8" Name="TierIndicator" PackLocation="cpc,top" PackLocationProp="0121/0370,0008/0001" PackSize="fixed,fixed" PackSizeProp="0002/0003,0002/0003" ScrollExtent="101,8" Size="101,8"/>
<Text AbsorbsInput="false" actiontype="Target" DynamicData="/GameData.Target.Name" Font="
/TextStyles.Small.SmallStyle" LocalText="Ambassador Rotgaf of Freeport" Location="251,16" MaximumSize="1700,1700" MaxLines="2" Name="Name" PackSize="absolute,fixed" PackSizeProp="0256/0001,0002/0003" ScrollExtent="114,25" ShadowStyle="/ShadowStyles.Outline1" Size="114,25" TextAlignment="Center" TruncateElipsis="false">Ambassador Rotgaf of Freeport</Text>
Now, those two areas that are highlighted in red will need to be changed. Simply change the word small to normal, or large depending on what you want. Remember to keep the capitalization the same as well.
If you choose to change the Implied Target as well, the file is eq2ui_mainhud_impliedtarget.xml. The two changes in that file will be the exact same as the two above for the target window.
I hope that I explained that ok. If not, let me know if you have any troubles.