See https://kb.projectmerge.org/swap-to-merge/swap-instructions and carry out the swap at https://swap.projectmerge.org. Discord is available at https://discord.gg/mAvgfdj.
Read the instructions carefully. You must send about half your amount to one address and half to another address - both will be given to you on the website.
Test first by sending a small amount to both addresses (e.g. 25 PNX) to make sure that it is working for you. The swap ratio is 57.14:1.
The deadline to swap is 15th March 2019 (see https://kb.projectmerge.org/swap-to-merge/coins-swapped).
Update (27th Feb): Swap transactions now appear to be working. Please test with a small amount first, but you should recieved your Merge a little after 50 confirmations.