I assume that by legal separation, you mean divorce?
You don't need legal representation for a divorce - you simply need to be separated for a period of at least 12 months before filing the documentation the court and the divorce is finalised after one month and one day from the hearing. A divorce hearing doesn't usually require attendance, but if there are kids under the age of 18 involved, you may need to go to the court on the day of the hearing to tell the registrar or judge what arrangements have been made for care of the kids.
The more strenuous part is the division of assets and care arrangements for the kids. You can self-represent through each of these matters as well, but as Sarah J pointed out, it can be highly stressful and daunting as it requires you to gain a sound knowledge of the Family Law Act 1975 and of court procedures.
Summarily, yes, you can give notice of dismissal of legal representation at any time in proceedings.