We're continuously adjusting purchase amount ones payment deducted from our account due to currency fluctuation. In current version of VAT we're not able to edit purchase because it has previously been included in a VAT Return and we cannot delete submitted VAT return from our side.
Once a VAT return has been submitted to HMRC it should not be altered in anyway as that is what has officially been recorded. In the rare circumstances where a VAT return may need to be deleted at HMRC request please contact Support@KashFlow.com who can arrange for the Development team to do that.