Business owner needs help.....

Hello There,
I am a business owner and not very experienced with MikroTik networks which is currently controls my business.
The system was set up by an IT personnel who went bad us and the relation is not very good. I do have and changed the admin password, however, I am worried about system abuse. Since there is no one at my organization familiar with MikroTik Systems, I was wondering, what additional pro-cations, if any, I must take in order the secure my network from expert abuse. I am certainly willing to approach this matter with a trustworthy and knowledgeable MikroTik expert on a business level. I would like to conduct communication trough “Private Messages”. Thank you kindly in advance.