An employer cannot change the terms of an employment contract unless the employee or their trade union representative agrees.
If you wish to change an employment contract as an employer, you can negotiate to see whether an agreement can be reached, for example, by offering financial compensation. We can advise you on making an offer to your employees and how you might go about altering a contract if they are amenable to change.
You will need to explain to the employees what effect the proposed changes will have. The employee should be given time to consider the proposals and be allowed to make alternative suggestions.