LE has introduced a whole new range of weapons, for every profession. However, they start off without any special, and a bit weak. For them to be of most use, they will need to be upgrade fully, a total of 5 times. The process is, however, relativelly simple.
You will first need to purchase your weapon. This can be done at any tower shop. Go to one of the new Ofab weapon terminal, and choose your weapon. They will need to be purchased with Victory Points, which you can get in either Alien Missions or in the BattleStation. This weapon will have the tag MK1, which you can upgrade to MK 6. Each upgrade will also have a new mesh.
The upgrades for each weapon are found in Alien Missions. They drop from the bosses. Here is the complete list.