Fidelity national information services Inc. FIS announced Thursday that it has accelerated its plan to split up into two companies by agreeing to sell a major stake in the Worldpay Merchant Solutions to GTCR-managed private equity funds in a transaction valued at $18.5 billion. FIS announced previously that it would spin off its Worldpay-dominated merchant business into a separate company. This move would reverse the merger between FIS and Worldpay announced in 2019. It said on Thursday that the agreement now reached will allow it to retain a…