If an FHA home loan is under water can it be changed to a conventional mortgage?

No but you may qualify for a FHA streamline refinance. Call your local mortgage company to inquire.

No you can not change it to a conventional mortgage. You can do an FHA streamline refinance. This process may not require an appraisal.

Only an FHA Streamline will work if you are underwater and currently have an FHA loan. You may be referring to a HARP loan, but those are only available for those that have a conventional loan. Fortunately, FHA Streamline does not require an appraisal.

You could refinance into an insured conventional and/or conventional so long as you're willing to bring sufficient enough cash to the closing table to get the principal loan to the appropriate loan-to-value for your needs. Good luck and have a great holiday weekend.