If you have a 4-prong 240 volt outlet but a 3-prong 240 volt cord on
your dryer, then you can put a 4-prong cord onto your dryer and it
will work with the existing outlet.

If you have a 120 volt outlet (such as what your washing machine would
plug into), then you can't exacly change the outlet for use by your
240 volt dryer; an electician would need to run a new line from the
breaker and build a complete new circuit and outlet for your dryer.
However, off the record, you can adapt a 240 volt dryer with a 120
volt power cord to plug into a 120 volt outlet, if you know how to
hook up the new cord to your dryer correctly. But just so you know,
your dryer will dry your clothes
reallllllllllllllllllllllllllllllllllly slow.