You can only import one data file into your Reep account (from a compatible accounting system).
Your clients would need their own Reep accounts and they would import their own data file from their accounting system. They would then create their budgets and share these budgets with you (i.e. not their file). For instructions on how to open a shared budget, click here.
You or your clients can edit the shared budgets. To delete the budgets, you must be the Reep account owner, or have access to the Reep account login details.