You cannot change the font of the tabs alone.
You can change the size of the tabs.
This is a function of your Windows Display Properties.
The size of the sheet tabs are governed by the setting for Scrollbars in
Windows Display Appearance. Mine are at 18. Start there and work your way
up or down. The font will increase or decrease with the size of sheet tabs.
Right-click on your Desktop and Properties>Appearance>Advanced
"Item" drop down select Scrollbar
Change setting to Taste
Apply
OK
Depending upon your settings, you may have to re-boot to see the changes.
Also note: this is a Global change and will affect all Applications.
Gord Dibben MS Excel MVP