You're not going to get spheres of colonization to switch complete Spain with England/UK and France with Portugal without switching the locations of those countries within Europe. However, here are some possibilities that could happen:
1) With a 15th-century POD you could potentially have Portugal and Castille switching roles in exploration. OTL Portugal was most interested in finding a route to Asia around Africa and Castille/Spain was more interested in colonizing the New World. Brazil only really happened because it was a stop on the way to the Cape of Good Hope. I think it wouldn't be difficult to have Castille be more interested in the route around Africa and Portugal more interested in the New World, although the Portugese don't have the population base to colonize it in the same way the Spanish did.
2) The Treaty of Tordesillas in 1494 was the original agreement which divided the world between Spain and Portugal and set up the original spheres of colonization. If this changes, you could see very different colonization. For example, during this time period latitidue was MUCH easier to measure than longitude so maybe rather than dividing the world East/West it could be divided North/South so that Portugal gets all lands South of the equator while Spain gets all lands to the North. This would still give Portugal what they want (a route around Africa to Asia) and Spain what they want (colonies in the region discovered by Columbus), so I think it could be plausible??
3) English and French colonial posessions could easily be switched if you pick the right POD. But at this point we're talking about a 16th century POD which would mean that Spain and Portugal's colonies would already be established. So, switching England with Spain and France with Portugal isn't going to happen.
4) There are two Personal Unions which reduced the number of potential colonial powers. Scotland could have been a colonial power separate from England if not for the Union of the Crowns. Similarly, Aragon could have been a colonial power separate from Castille if Ferdinand and Isabella had never married. I can't see Scotland or Aragon establishing colonies to the same extend as England or Castille, but they could potentially colonize as much as the Portugese or the Dutch....
5) I'd LOVE to see a TL in which Ireland, Wales, Brittany, or Navarre has colonies, but this would require a MUCH earlier POD (14th century or earlier). But, all four of these are placed in good locations for sea voyages out into the Atlantic (in particular, Britanny was the base for many of the French explorers).
