How do you accelerate transactions?
You can found a lot free service that offer accelerate transaction in service section. But you can try this one
https://pool.viabtc.com/tools/txaccelerator/ , just simple copy and paste your txid and put it on there.
What doesn't that mean? Adding additional miner fee after it's been sent?
Umm... Its looks like your transaction will be prioritise by miner. Something like that.