how do I take a good quality photo to blow it up to 16X20 or 20X30

You do not unless you have a printer that size - the print size is set by the printing service - send a photo that meets the printer's requirements to the printer of your choice and they will print it the size you order

LN

What are the pixel dimensions of your photo? It depends on what you consider good quality.

Printing at home I try to print at 300 dpi. An 8 x 10 photo should have a dimensions of 2400 pixels x 3000 pixels and a 16 x 20 whould be double that, 4800 x 6000.

I've printed photos at 150 dpi so the same 2400 x 3000 image would print a 15 x 20 poster reasonable well. Again it depends on your expectations,.

I created a collage, 20 x 30, with 96 photos at 300 dpi (6000 x 9000) and had it printed at a place in Los Angeles at a reasonalbe price. It was mounted on foam board. The one aspect of this LA printer is that they wanted the file to have the CMYK profile. Well, that can be achieved with Photoshop (which I used) or GraphicConverter (the demo mode will convert a file to CMYK). I've ordered a number of large size prints from them with great success - Digital Printing Service and Company | Digital Room.

Also local printing shops like Kinkos can give you good prints also but I think sRGB color profile may be needed. Be sure to check with whomever you choose.

OT