Just wait and hodl, if BTC goes up now, alts will naturally go down until BTC reaches a sustained uptrend, then they will go up if they should. Explanation is buyer/seller are all on main coins, then when the uptrend is on, some buyers will go to alts just because they hodl BTC and they want to diversifie.
If BTC goes down again (correction not done) alt will go up, if you're happy with profit, take it, or wait for more after BTC goes in uptrend (take more time of course).
Anyway you can sell altcoins for some USD equivalent on a lot of exchanges, problem is if BTC goes up you'll get less of it because BTC/USD goes up.
Better is wait and see, if btc down => sell alt if profit ok or wait for btc uptrend and in phase with alt, else if btc up wait for alt and btc to be in phase and take profit when ok.
At least that's what I'm doing. If alts are well selected, they should go up, maybe it will take some weeks but they will go up.