You NEED to see how the freezer is connected to the wall. If it's a normal 3 pin socket you are OK, you will be able to just plug-in the new one. If it's the sort in my link you can connect it yourself IF YOU ARE COMPETENT. There is no legal requirement to get an electrician to do it but, if you don't understand electricity, you need to get someone who does to do it for you. If you get an electrician in you might want to change the wall connection to a normal 3-pin outlet (and put a normal plug on the current freezer); that way you can get the job done now and it will be straightfoeward when you come to swap freezers.