How to update multiple values to a list item.

Hi guys,

can some one give me an advice, how can I update multiple values to an list item related to a user.
e.g.:

employees add there Holidays, userA and he has 30days/year it for Dynamic Holiday Calculating.

1. UserA from 14.07.2014 to 20.07.2014 e.g. 6 days
2. UserA from 07.08.2014 to 23.08.2014 e.g. 16 days
3. UserA from 02.09.2014 to 06.09.2014 e.g. 4days
etc.

NOW I want Edit the first item I want take 3 days instad of 6 days, because the items calculatiting based on eachother I must update thesuccessor and dont need to update thepredecessor.

Whats the best Appraoch?

Workflow/Event Receiver or if someone have better idea.

thanks in advance

BR

Ahmad

SP 2013 & SPD 2013 & VS 2013 & MSSQL 2012