Enlargements generally are frowned upon by FAA - as they introduce a great deal of blur - a printer's nightmare.
Topaz GigaPixel can make successful upscales - which with judicial handling - can be kept printer sharp.
Post your upscaled work here - for a discussion as to how to keep it sharp - and sharp enough to print.
Any format or media. N.B. as Topaz GigaPixel is new software - there is in all likelihood a steep learning curve!
Do not feel 'knocked-back' if you post work in this Group which is not sharp enough.
Try, try and try again is the motto - for it is only in making mistakes that we can learn and improve our art!