It is a personal choice if you want to combine your retirement accounts from your previous employers. Sometimes people like to combine their old employer retirement accounts so that the retirement money is in one account. Also, you may have more investment choices in a Rollover IRA account than you would in a former employer 401k plan. If you want to do this you would need to open a Rollover IRA account and request the custodian's of the accounts that you want to move to do a rollover directly to the newly established Rollover IRA account. If this is done properly the rollover would not be a taxable event.
All the best,
AnthonyC_CPA