Is there a possibility i can ammend some CSS or something to increase the text size on Upload.aspx? I guess not but it would be very nice if i could.
Any advice would be great, we are using SharePoint Online 365 .
Yes, there is a possibility, however, this way will change the upload forms all over your Site Collection.
You can add following Code to your masterpage:
Mind to change the selector (
#element ) to the DOM-Element, which should be changed (You can find it via the Hover-Tool using Webbrowser-Dev-Tools).
Example: You want to change the font-size of "Datei auswählen":
Then the correct selector is: