There are two ways to do this. Firstly, highlight the text that needs resizing then highlight the number in the font box and overtype the size you want to increase to, noting that .5 can be used. Secondly, you can highlight the text concerned then press Control + [ to decrease or Control + ] to increase the font by one number.
The pt system has 2 types both similar The true type pt system has 72 increments to the inch (24.4mm) The post script pt system has slightly more at 72.2 increments to the inch. Some will say it doesnt matter but if you are writing a book and the printer sets the type with a post script type setter the book will get longer by 1 ot 2 pages per 100 A4 pages.
To print 2 inch characters use 144pt type. I use Adobe Illustrator and have used type of 250pt before now
You can go any size you want. Open your Word and click in the size window (that usually says 10 or 12) so that it is highlighted, then type in 500 and hit enter. Any text now typed will be VERY large.