"Greg and Kelly Carr" wrote:

I took apart an existing wall in my home and found that 15 amp outlets were
used on a 20 amp circuit. Should these be replaced with 20 amp?

No. A 20 amp single load needs a 20amp plug, which won't fit in a 15 amp
outlet (one of the lugs is twisted). These are uncommon in the US,
usually only big heaters will have a 20 amp plug.

Unless you have a load that won't fit the outlet, you won't gain
anything by switching.