It is feasible to go for a refinance when you have built up at least 10% equity in your home (For Fannie Mae owned mortgages, the value is 5%). It is also possible for you to choose the option if your equity is less than 5%, but you may have to pay a certain amount of cash in order to make up for the difference in equity.
When refinancing, don't take the first offer that comes around. Instead you should actively compare both interest rates and lenders.
Refinancing a mortgage means the owners are paying off their existing mortgage and replacing that mortgage with a new loan. Generally, the costs associated with mortgage refinancing are rolled into the loan, meaning they are added to the existing balance, increasing the loan amount.
If there are only a few years left on your current loan, it's no use refinancing with a long term loan. You may need extra cash but with a long term loan, you'll end up paying more for the entire loan term.