getting rid of a percentage split

I assume you're referring to a Memorized Payee, that has "%Spl" in the Type column in the Memorized Payee List.

If you still have the original register transaction from which you memorized the payee:

- delete the existing memorized payee

- right-click the existing register transaction

- choose "Memorize payee ..." and answer "No" when asked "Memorize split payees as percentages?".

If you no longer have the original transaction from which you memorized the payee (this will not necessarily be less work than just recreating the memorized payee from scratch):

- open an appropriate account register

- open the Memorized Payee List

- right-click the appropriate memorized payee and choose "Use"

- enter the fixed amount you want the ultimate memorized payee to have, and click OK

- in the "appropriate account register", right-click the newly entered transaction

- choose "Memorize payee ..." and answer "No" when asked "Memorize split payees as percentages?"

- delete the newly entered transaction

To clarify, the last point should read, "- delete the newly entered REGISTER transaction".