php - Yii application vs User loads -

i have created crm application using yii framework, works when user less, when user connected increases above 250 users, the performance of application slow,

i have tested via load impact, can able test 100 users

can suggest how rid of issue ?

this scaling problem. have few options:

1. scale up: upgrade server higher configuration. (need $$$)
2. scale out: deploy app more 1 servers , configure load balancer distribute traffic them. may need centralized session store (e.g. yii\redis\session) ensure sessions persist across different nodes. (need $$$ + time)
3. optimize app: review code find out parts slow , see if can optimized. (need time)

which 1 best depends on situations (e.g. money / time / technical knowledge or team)