Hello @Claymenia
First of all, I have to inform you that we haven’t tested installation of Document Server on Synology NAS. However, if you can confirm that the provided by you guide works with Community Edition, then it is quite easy to install Enterprise Edition.
Before taking action one important note: there is no upgrade process from one edition to another. You simply have to re-install Document Server but of needed edition.
Basically, you have to remove your current Community Edition and then go through the same shared guide but on the step 14-3/3 use this code instead of suggested one to install Enterprise Edition:
docker run -d --name=OnlyOffice \
-p 8467:80 \
-v /volume1/docker/onlyoffice/logs:/var/log/onlyoffice \
-v /volume1/docker/onlyoffice/data:/var/www/onlyoffice/Data \
-e JWT_ENABLED=true \
-e JWT_SECRET=JWT \
--restart always \
onlyoffice/documentserver-ee
After that, go to the Welcome Page of Document Server via its address and check if it correctly says ONLYOFFICE Docs Enterprise Edition installed in the title. If it does, then installation was successful and now you have to activate your product with the license according to this official guide:
https://helpcenter.onlyoffice.com/installation/docs-enterprise-activation.aspx