You get a copy of your parents' will in the mail, after they pass away, and you simply do not like it. Some of the provisions do not sit well with you. Maybe it instructs you and your siblings to sell the house and divide the profits, when you wanted to keep the house. Maybe it gives money to a sibling that you know will simply waste that money, or perhaps it does not leave you as much as you expected.
Can you challenge it just because you don't like it?
Typically, you cannot. Even if you do not like a single provision in the will, that's not reason enough to start a challenge.
Instead, you need to know why the will could be invalid. What led to those provisions you do not like that may also stand up in court? Simply complaining that your parents did not do what you wanted them to do isn't going to get the will overturned.
For instance, maybe you did not get as much money as your siblings. However, they live closer to your parents, while you live out of state. In an earlier will, you all got equal amounts, but your parents altered the will within the last year. You believe that they only did it because your siblings used undue influence or took advantage of your parents' deteriorating mental state to get them to make changes they did not really want to make.
If so, then you may have the right to contest the will. It is very important to understand exactly what legal steps you need to take.