No, you don't need to make a new Will. If you are happy that your current Will still reflects your wishes and you simply wish to make some additions or small changes, then your Solicitor can help create a Codicil. 

What is codicil in a Will?  A codicil is a legal document that acts as a supplement to your last will and testament. In it, you can make changes to your will without having to rewrite your entire original Will document.

However, it is a good idea to regularly review your Will, to ensure it reflects any changes in your circumstances (e.g. marriage, a new house, children and grandchildren).