Does anyone know how to replace the in-dash speakers on a 1994 GMC Sierra?

[idleford97]

I need to replace the in dash speakers on a 1994 GMC Sierra pickup . The panels on the dash do have some movement , do they just pop off or do I have to pull the dash? Does anyone know what size they actually are? Crutchfield.com list them at 4x6 but then it shows 3 1/2" and list them as "IT FITS" . So does it take 4x6 or 3 1/2"?