Replication – Optimization, Increasing Time Out. Problem

Can anybody help with any advice on how to optimize replication?
The set up: 2 Agents: merge and distribution are set up. Clients log in to VPN e every day to perform Replication.
It was going very well. However recently for the reason of DB growth(I think) it started to time out more and more.

I am not DB admin but a developer, any advice could be appreciated. I already increased TimeOut option, I need to try something also.

Appreciate any help.!!