You may find a new chain will skip over some of the rear cassette cogs, depending on how worn the old chain is, best to measure it first then make a call on whether you are up for both. Do you regularly clean and lube the drive chain? Rule of thumb is chain and cassette wear together and if the chain is changed in time you will not have any issues with chain skipping but if its left too late you have to change both together there are a zillion and 1 threads on this subject so do some research.